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FRANCA MANGHI

DIPENDENTE ALTRO ENTE DI RICERCA
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2017 - Dynamics and control of edge states in laser-driven graphene nanoribbons [Articolo su rivista]
Puviani, Matteo; Manghi, F.; Bertoni, A.
abstract

An intense laser field in the high-frequency regime drives carriers in graphene nanoribbons (GNRs) out of equilibrium and creates topologically protected edge states. Using Floquet theory on driven GNRs, we calculate the time evolution of local excitations of these edge states and show that they exhibit a robust dynamics also in the presence of very localized lattice defects (atomic vacancies), which is characteristic of topologically nontrivial behavior. We show how it is possible to control them by a modulated electrostatic potential: They can be fully transmitted on the same edge, reflected on the opposite one, or can be split between the two edges, in analogy with Hall edge states, making them promising candidates for flying-qubit architectures.

2017 - Theory of photon-driven correlated electrons in one dimension [Relazione in Atti di Convegno]
Puviani, M.; Manghi, F.
abstract

In this paper we present a general theoretical framework to study interacting electrons under the influence of an external time-periodic driving, such as a homogeneous laser field. This is performed through a true many-body calculation and the use of Floquet theory. In particular, we consider a linear atomic chain using the Hubbard model to describe the short-ranged Coulomb interactions between electrons, plus Cluster Perturbation Theory to embed the many-body exact solution for a finite system into both an extended and an infinite lattice. Due to the presence of the external time-periodic perturbation, the electronic problem can be mapped into the study of photon-dressed quasiparticles thanks to Floquet theorem, keeping into account of all the virtual processes (absorption and emission of photons by electrons) with the laser field. This leads to an extension of the many-body static theories to out-of-equilibrium systems. This theoretical approach allowed us to show how the electronic properties of the system can be controlled and tuned varying the laser parameters. Above all, an inverse insulator-to-metal transition can be obtained for the one dimensional infinite lattice, and edge localized states appear as a finite size effect in an extended truncated chain.

2016 - Heterodimers of heterometallic rings [Articolo su rivista]
Timco, Grigore; Marocchi, Simone; Garlatti, Elena; Barker, Claire; Albring, Morten; Bellini, Valerio; Manghi, Franca; Mcinnes, Eric J. L.; Pritchard, Robin G.; Tuna, Floriana; Wernsdorfer, Wolfgang; Lorusso, Giulia; Amoretti, Giuseppe; Carretta, Stefano; Affronte, Marco; Winpenny, Richard E. P.
abstract

Nine new complexes are reported involving linked heterometallic rings; one ring is designed as a ligand for the second, and the compounds produced can be regarded as molecular prototypes for implementing quantum gates featuring two subtly different qubits.

2016 - Periodically driven interacting electrons in one dimension: Many-body Floquet approach [Articolo su rivista]
Puviani, M.; Manghi, F.
abstract

We propose a method to study the time evolution of correlated electrons driven by a harmonic perturbation. Combining Floquet formalism to include the time-dependent field and cluster perturbation theory to solve the many-body problem in the presence of short-range correlations, we treat the electron double dressing, by photons and by e-e interactions, on the same footing. We apply the method to an extended Hubbard chain at half occupation, and we show that in the regime of small field frequency and for given values of field strength, the zero-mode Floquet band is no longer gapped and the system recovers a metallic state. Our results are indicative of an omnipresent mechanism for insulator-to-metal transitions in one-dimensional systems.

2015 - Quasiparticle band structure [Articolo su rivista]
Manghi, Franca; Boni, Valentina
abstract

Many body effects influence the energy-versus-momentum relation that is measured in angle resolved photoemission experiments and the quasiparticle band structure may be significantly different from what is deduced within the independent particle model. In the case of cobalt many body effects are even more drastic than an energy renormalization giving rise to a quenching of quasiparticle peaks. Augmenting ab-initio band structure with many-body e-e interactions we have obtained spin- and k-dependent self-energies, hole spectral functions and quasiparticle energies to be compared with photoemission spectra; our results show that e-e correlations are responsible for strong spin-dependent energy renormalizations.

2015 - Topological invariants in interacting quantum spin Hall: a cluster perturbation theory approach [Articolo su rivista]
Grandi, F.; Manghi, Franca; Corradini, Olindo; Bertoni, Carlo Maria; Bonini, Alfredo
abstract

Using cluster perturbation theory we calculate Greenʼs functions, quasi-particle energies and topological invariants for interacting electrons on a 2Dhoneycomb lattice, with intrinsic spin–orbit coupling and on-site e–e interaction. This allows us to define the parameter range (HubbardUversus spin– orbit coupling) where the 2D system behaves as a trivial insulator or quantum spin Hall insulator. This behavior is confirmed by the existence of gapless quasi-particle states in honeycomb ribbons.Wehave discussed the importance of the cluster symmetry and the effects of the lack of full translation symmetry typical of CPT and of most quantum cluster approaches. Comments on the limits of applicability of the method are also provided.

2015 - Topological properties of the bond-modulated honeycomb lattice [Articolo su rivista]
Grandi, F.; Manghi, Franca; Corradini, Olindo; Bertoni, Carlo Maria
abstract

We study the combined effects of lattice deformation, e−e interaction, and spin-orbit coupling in a two-dimensional (2D) honeycomb lattice. We adopt different kinds of hopping modulation—generalized dimerization and a Kekulé distortion—and calculate topological invariants for the noninteracting system and for the interacting system. We identify the parameter range (Hubbard U, hopping modulation, spin-orbit coupling) where the 2D system behaves as a trivial insulator or quantum spin Hall insulator.

2014 - DFT Study of the Cr8 Molecular Magnet Within Chain-Model Approximations [Relazione in Atti di Convegno]
Bellini, Valerio; Daria, M. Tomecka; Brzostowski, Bartosz; Wojciechowski, Michał; Troiani, Filippo; Manghi, Franca; Affronte, Marco
abstract

We present a density functional theory (DFT) study of the electronic and magnetic properties of the Cr8 molecular ring. The allelectron linearized augmented plane wave method (LAPW) implemented in the Wien2k package and pseudopotential method implemented in SIESTA package are used to calculate the electronic states, exchange coupling parameters of an infinite chain model system of Cr8.We demonstrate how, under opportune modifications to the ring cycle structure, different one-dimensional chain models can be devised, with the capability of mimicking with good approximation the electronic and magnetic properties of the original Cr8 molecule. Such models offer an unique opportunity, in virtue of the reduced computational effort, to carry out extensive investigations of a whole set of molecules belonging to the Crbased molecular rings family.

2014 - Multi-orbital cluster perturbation theory for transition metal oxides [Articolo su rivista]
Manghi, Franca
abstract

We present an extension of cluster perturbation theory to include many-body correlations associated with local e-e repulsion in real materials. We show that this approach can describe the physics of complex correlated materials where different atomic species and different orbitals coexist. The prototypical case of MnO is considered.

2014 - Reentrant metallicity in the Hubbard model: the case of honeycomb nanoribbons [Articolo su rivista]
Manghi, Franca; Petocchi, F.
abstract

Based on the cluster perturbation solution of the Hubbard Hamiltonian for a 2D honeycomb lattice, we present quasi-particle band structures of nanoribbons at half filling as a function of on-site electron-electron (e-e) repulsion. We show that, at moderate values of e-e interaction, ribbons with armchair-shaped edges exhibit an unexpected semimetallic behavior, recovering the original insulating character only at larger values of U.

2013 - Graphene-mediated exchange coupling between a molecular spin and magnetic substrates [Articolo su rivista]
S., Marocchi; P., Ferriani; N. M., Caffrey; Manghi, Franca; S., Heinze; V., Bellini
abstract

Using first-principles calculations we demonstrate sizable exchange coupling between a magnetic molecule and a magnetic substrate via a graphene layer. As a model system we consider cobaltocene (CoCp2) adsorbed on graphene deposited on Ni(111). We find that the magnetic coupling is antiferromagnetic and is influenced by the molecule structure, the adsorption geometry, and the stacking of graphene on the substrate. We show how the coupling can be tuned by the intercalation of a magnetic monolayer, such as Fe or Co, between graphene and Ni(111). We identify the leading mechanism responsible for the coupling to be the spatial and energy matching of the frontier orbitals of CoCp2 and graphene close to the Fermi level. Graphene plays the role of an electronic decoupling layer while allowing effective spin communication between molecule and substrate.

2012 - Effects of spin-dependent quasiparticle renormalization in Fe, Co, and Ni photoemission spectra:An experimental and theoretical study [Articolo su rivista]
J., Sánchez Barriga; J., Braun; J., Minár; I., Di Marco; A., Varykhalov; O., Rader; V., Boni; V., Bellini; Manghi, Franca; H., Ebert; M. I., Katsnelson; A. I., Lichtenstein; O., Eriksson; W., Eberhardt; H. A., Dürr; J., Fink
abstract

We have investigated the spin-dependent quasiparticle lifetimes and the strength of electron correlation effects in the ferromagnetic 3d transition metals Fe, Co, and Ni by means of spin- and angle-resolved photoemission spectroscopy. The experimental data are accompanied by state-of-the-art many-body calculations within the dynamical mean-field theory and the three-body scattering approximation, including fully relativistic calculations of the photoemission process within the one-step model. Our quantitative analysis reveals that inclusion of local many-body Coulomb interactions are of ultimate importance for a realistic description of correlation effects in ferromagnetic 3d transition metals. However, we found that more sophisticated many-body calculations with larger modifications in the case of Fe and Co are still needed to improve the quantitative agreement between experiment and theory. In general, it turned out that not only the dispersion behavior of energetic structures should be affected by nonlocal correlations but also the line widths of most of the photoemission peaks are underestimated by the current theoretical approaches. The increasing values of the on-site Coulomb interaction parameter U and the band narrowing of majority spin states obtained when moving from Fe to Ni indicate that the effect of nonlocal correlations becomes weaker with increasing atomic number, whereas correlation effects tend to be stronger.

2012 - First-principles calculation of x-ray dichroic spectra within the full-potential linearized augmented planewave method: An implementation into the Wien2k code [Articolo su rivista]
L., Pardini; V., Bellini; Manghi, Franca
abstract

X-ray absorption and its dependence on the polarization of light is a powerful tool to investigate the orbital and spin moments of magnetic materials and their orientation relative to crystalline axes. Here, we present a program for the calculation of dichroic spectra from first principles. We have implemented the calculation of X-ray absorption spectra for left and right circularly polarized light into the Wien2k code. In this package, spin-density functional theory is applied in an all-electron scheme that allows to describe both core and valence electrons on the same footing. The matrix elements, which define the dependence of the photo-absorption cross-section on the polarization of light and on the sample magnetization, are computed within the dipole approximation. Results are presented for the L2,3 and M4,5 egdes of CeFe2 and compared to experiments.

2011 - Effects of electronic correlation on x-ray absorption and dichroic spectra at L-2,(3) edge [Articolo su rivista]
L., Pardini; V., Bellini; MANGHI, Franca
abstract

We present a new theoretical approach to describe x-ray absorption and magnetic circular dichroism spectra in the presence of electron-electron correlation. Our approach provides an unified picture to include correlations in both charged and neutral excitations, namely in direct/inversion photoemission where electrons are removed/added, and photoabsorption where electrons are promoted from core levels to empty states. We apply this approach to the prototypical case of the L-2,(3) edge of 3d transition metals and we show that the inclusion of many-body effects in the core level excitations is essential to reproduce, together with satellite structures in core level photoemission, the observed asymmetric lineshapes in x-ray absorption and dichroic spectra.

2011 - Interfacial magnetic structure in Fe/NiO(001) [Articolo su rivista]
Luches, P.; Pasquini, L.; Benedetti, S.; V. Bellini V., ; Valeri, Sergio; Manghi, Franca; Ruffer, R.; Boscherini, F.
abstract

Using nuclear resonant scattering of synchrotron radiation and density functional theory calculations we haveresolved the magnetic properties of the different Fe phases present at the Fe/NiO(001) interface, an epitaxialferromagnetic/antiferromagnetic system. We have detected the presence of an interfacial antiferromagneticFeO-like phase with a significantly increased magnetic moment compared to the case of a sharp interface.Already a few atomic layers above the interface, the Fe atoms have a bulk-like metallic character and the reversalof their magnetization is strongly influenced by the antiferromagnetic layer.

2011 - XMCD Spectra Based on DensityFunctional Theory [Capitolo/Saggio]
L., Pardini; Manghi, Franca; V., Bellini; C., Ambrosch Draxl
abstract

In this Chapter, we discuss how to treat XMCD spectra for solidsfrom first-principles by employingdensity functional theory(DFT) . To this aim we will firstintroduce the reader to the basics of DFT as well as to thelinearized augmented planewave (LAPW) method , which is our method of choice tosolve the corresponding single-particle equations. Thereafter, wewill describe how to obtain the scattering cross section withinFermi's golden rule, and how thisapproach has been implemented into the LAPW method. Finally, we willgive results for the transition metals iron, cobalt, and nickel. Wewill compare the XMCD spectra with experiments and show the impact ofmany-body effects as obtained within the three-body scattering theory.

2010 - Quantitative determination of spin-dependent quasiparticle lifetimes and electronic correlations in hcp cobalt [Articolo su rivista]
J., Sánchez Barriga; J., Minár; J., Braun; A., Varykhalov; Boni, Valentina; I., Di Marco; O., Rader; V., Bellini; Manghi, Franca; H., Ebert; M. I., Katsnelson; A. I., Lichtenstein; O., Eriksson; W., Eberhardt; H. A., Dürr; J., Fink
abstract

We report on a quantitative investigation of the spin-dependent quasiparticle lifetimes and electron correlation effects in ferromagnetic hcp Co(0001) by means of spin- and angle-resolved photoemission spectroscopies. The experimental spectra are compared in detail to state-of-the-art many-body calculations within the dynamical mean-field theory and the three-body scattering approximation, including a full calculation of the one-step photoemission process. From this comparison we conclude that although strong local many-body Coulomb interactions are of major importance for the qualitative description of correlation effects in Co, more sophisticated many-body calculations are needed in order to improve the quantitative agreement between theory and experiment, in particular, concerning the linewidths. The quality of the overall agreement obtained for Co indicates that the effect of nonlocal correlations becomes weaker with increasing atomic number.

2009 - Photo-excitation of a light-harvesting supra-molecular triad: a Time-Dependent DFT study [Articolo su rivista]
Nicola, Spallanzani; CARLO ANDREA, Rozzi; Daniele, Varsano; Tunna, Baruah; Mark, Pederson; Manghi, Franca; Angel, Rubio
abstract

We present the first time-dependent density functional theory (TDDFT) calculation on a light-harvesting triad carotenoid-diaryl-porphyrin-C-60. Besides the numerical challenge that the ab initio study of the electronic structure of such a large system presents, we show that TDDFT is able to provide an accurate description of the excited-state properties of the system. In particular, we calculate the photoabsorption spectrum of the supramolecular assembly, and we provide an interpretation of the photoexcitation mechanism in terms of the properties of the component moieties. The spectrum is in good agreement with experimental data, and provides useful insight on the photoinduced charge-transfer mechanism which characterizes the system.

2009 - Strength of Correlation Effects in the Electronic Structure of Iron [Articolo su rivista]
J., Sánchez Barriga; J., Fink; BONI, VALENTINA; I., Di Marco; J., Braun; J., Minár; A., Varykhalov; O., Rader; V., Bellini; MANGHI, Franca; H., Ebert; M. I., Katsnelson; A. I., Lichtenstein; O., Eriksson; W., Eberhardt; H. A., Dürr
abstract

The strength of electronic correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) has been investigated by means of spin and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. This comparison indicates that the present state of the art many-body calculations, although improving the description of correlation effects in Fe, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations.

2008 - Ab initio study on a chain model of the Cr8 molecular magnet [Articolo su rivista]
D. M., Tomecka; V., Bellini; F., Troiani; Manghi, Franca; G., Kamieniarz; Affronte, Marco
abstract

We present a density-functional theory investigation of the electronic and magnetic properties of a linear chain model of the antiferromagnetic Cr8 molecular ring. The chain model system is characterized by a smaller size of the simulation cell needed to perform the calculations, with respect to the one necessary for Cr8. By the thorough comparison between the model complex and the Cr8 ring, we prove that the chain model is reliable and mimics with good approximation the electronic and magnetic properties of Cr8.

2007 - ARPES band maps of ferromagnetic iron: Theoretical simulation including e-e correlation [Abstract in Atti di Convegno]
Manghi, Franca; Bellini, V; Rozzi, Ca
abstract

Many-body effects influence the energy-versus-momentum relation that is measured in angle resolvedphotoemission experiments and the quasiparticle band structure may be significantly differentfrom what is deduced within the independent particle model. Stimulated by recent high resolutionphotoemission data for iron showing quasiparticle renormalization close to the Fermi energy [1] wehave performed a systematic study 3d transition metals including on-site e-e correlation within the3Bs approach [2]; this amounts to solve a multi-orbital Hubbard Hamiltonian through an expansionof the interacting state in terms of configurations with one electron-hole pair added to the non interactingground state. The systematic analysis of metals of the 3d transition series allow us to showthat band occupation is a key parameter to quantify the effectiveness of many-body interactions. Wefind that e-e correlations are responsible for spin-dependent energy renormalization; in iron it turnsout that empty minority spin states are most affected while the same is true for filled majority spinones. A detailed analysis of energy dispersion curves after the inclusion of many body correctionand a comparison with measured spectra is also shown.

2007 - Ab initio study of the Fe∕NiO interface: Structural and magnetic properties [Articolo su rivista]
V., Bellini; L., Di Giustino; Manghi, Franca
abstract

The structural and magnetic properties of the Fe/NiO(100) interface have been theoretically studied by density-functional theory within generalized gradient approximation (GGA) and, in selected cases, GGA+U methods. By total energy calculation, we find that Fe atoms adsorb preferentially on O sites and that a chemical reduction of NiO occurs, giving rise, for adsorption of more than one monolayer, to an interface of complex chemical and structural compositions, characterized by oxygen migration toward the surface. The magnetic moments at the interface and their alignment in a ferromagnetic and/or antiferromagnetic ordering are deeply influenced by the geometrical configuration of the atoms, pointing out to an important interplay between structure and magnetic configuration. This mechanism, at small oxidation level, leads quite naturally to the appearance of uncompensated spins at the interface.

2007 - Theoretical simulation of core level photoemission in transition metal oxides [Abstract in Atti di Convegno]
Manghi, Franca; Rozzi, Ca; CALANDRA BUONAURA, Carlo
abstract

core level

2006 - Correlation effects on the electronic properties of Bi2Sr2CaCu2O8 [Articolo su rivista]
Bellini, V; Rozzi, Ca; Manghi, Franca
abstract

We have studied the role of on-site electronic correlation on the band structure of Bi2Sr2CaCu2O8. In our approach, an ab initio calculation supplies for the single particle starting point, on top of which self-energy effects are explicitly taken into account in the framework of the three-body scattering theory (3BS). We observe that correlation modifies the energy dispersion of hole quasiparticle states near the Fermi level, especially close to the X and (M) over bar symmetry points, but does not induce sensible changes at the Fermi level. To sustain this picture, we report calculations of effective masses.

2006 - Density-functional study of the Cr-8 antiferromagnetic ring [Articolo su rivista]
Bellini, V; Olivieri, A; Manghi, Franca
abstract

We present the results of an ab initio characterization of the electronic and magnetic properties of the Cr-8 molecular ring. The original molecule with formula [Cr(8)F(8)Piv(16)](HPiv=pivalic acid, trimethyl acetic acid) has been approximated by replacing the disordered methyl groups by H atoms, obtaining de facto the formula [Cr8F8(O2CH)(16)]. We find in agreement with experiments that the Cr atoms attain a local spin moment of 3/2, and that the preferred arrangement of Cr atoms in the ground state is antiferromagnetic. By the total energy difference we calculate the value of the isotropic Heisenberg exchange parameter and we show that only after the inclusion of on-site correlation effects in the Cr d orbitals the value deduced by specific heat and torque measurements is recovered.

2006 - Iron oxidation, interfacial expansion, and buckling at the Fe/NiO(001) interface [Articolo su rivista]
Luches, P; Bellini, V; Colonna, S; Di Giustino, L; Manghi, Franca; Valeri, Sergio; Boscherini, F.
abstract

In order to provide a structural basis for a physical understanding of exchange bias in metal/magnetic-oxide interfaces, we have determined the structure of the Fe/NiO(001) interface by means of x-ray absorption spectroscopy and ab initio density functional theory calculations. A Fe-Ni alloyed phase on top of an interfacial FeO planar layer is formed. The FeO layer exhibits a 7% expanded interlayer distance and a 0.3 angstrom buckling; its presence is predicted to increase the spin magnetic moment of the interface Fe atoms by 0.6 mu(B), compared to the ideally abrupt interface.

2005 - First-principle theory of correlated transport through nano-junctions [Articolo su rivista]
Ferretti, Andrea; Calzolari, Arrigo; DI FELICE, Rosa; Manghi, Franca; M. J., Caldas; M., BUONGIORNO NARDELLI; Molinari, Elisa
abstract

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of shortrange interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.

2005 - First-principles theoretical description of electronic transport including electron-electron correlation [Articolo su rivista]
A., Ferretti; A., Calzolari; R., Di Felice; Manghi, Franca
abstract

We report about the inclusion of many-body electron interactions in the simulation of transport properties. We derive a general Landauer-like expression for the current, valid also in the case of conductors in which the charge carriers undergo generic scattering processes. An important focus is put on the derivation of the theoretical framework, both for the general formalism and for the actual implementation of the method, including the treatment of electronic correlation. We then show an example of application and compare the results on the electronic and conduction properties obtained with our new scheme to those given by alternative computational frameworks.

2005 - Theoretical simulation of core-level photoemission in transition-metal oxides [Articolo su rivista]
Rozzi, Ca; Manghi, Franca; CALANDRA BUONAURA, Carlo
abstract

We discuss the 2p and 3s line shape in NiO and MnO photoemission, and we show that the main features of all the spectra for both systems are reproduced within an unique theoretical scheme that takes into account the dynamics of the created photohole, together with the detailed band structure of the compounds. The solid state bonding and the antiferromagnetic order are found to deeply influence the characteristics of core level spectra; in particular, the large difference in the spin unbalance of MnO and NiO explains the different response of the two compounds to the creation of a core hole.

2004 - Coordination dependence of hyperfine interactions at impurities on fcc metal surfaces. I. Electric-field gradient [Articolo su rivista]
V., Bellini; S., Cottenier; M., Cakmak; Manghi, Franca; M., Rots
abstract

We present a comparison between accurate ab initio calculations and a high-quality experimental data set (1986-2002) of electric-field gradients of Cd at different sites on Ni, Cu, Pd, and Ag surfaces. Experiments found a systematic rule to assign surface sites on (100) and (111) surfaces based on the main component of the electric-field gradient, a rule that does not work for (110) surfaces. Our calculations show that this particular rule is a manifestation of a more general underlying systematic behavior. When looked upon from this point of view, (100), (111) and (110) surfaces behave in precisely the same way. The physical mechanism behind the systematics of the EFG for other 5sp impurities (Cd-Ba) at different fcc surfaces sites is revealed, showing in a natural way why the first half of the 5p elements shows a coordination dependence that is opposite with respect to the second half.

2004 - Coordination-dependence of hyperfine interactions at impurities on fcc metal surfaces. II. Magnetic hyperfine field [Articolo su rivista]
V., Bellini; S., Cottenier; M., Cakmak; Manghi, Franca; Rots, AND M.; PHYSICAL REVIEW, B.
abstract

We present a comparison between ab initio calculations and a high-quality experimental data set (1990–2002) of magnetic hyperfine fields of Cd at different sites on Ni surfaces. The experimentally observed parabolic coordination number dependence of this hyperfine field is verified as a general trend, but we demonstrate that individual cases can significantly deviate from it. It is shown that the hyperfine fields of other 5sp impurities at Ni surfaces have their own, typical coordination number dependence. A microscopic explanation for the different dependencies is given in terms of the details of the s-DOS near the Fermi level.

2004 - Molecular phases in coupled quantum dots [Articolo su rivista]
M., Rontani; S., Amaha; K., Muraki; Manghi, Franca; Molinari, Elisa; S., Tarucha; D. G., Austing
abstract

We present excitation energy spectra of few-electron vertically coupled quantum dots for strong and intermediate interdot coupling. By applying a magnetic field, we induce ground state transitions and identify the corresponding quantum numbers by comparison with few-body calculations. In addition to atomiclike states, we find novel "molecularlike" phases. The isospin index characterizes the nature of the bond of the artificial molecule and this we control. Like spin in a single quantum dot, transitions in isospin leading to full polarization are observed with increasing magnetic field.

2004 - Spin dependent many-body effects in the photoemission of Co [Articolo su rivista]
Manghi, Franca; Bellini, V; Rozzi, Ca
abstract

Many-body effects influence the energy versus momentum relation that is measured in angle-resolved photoemission experiments and the quasi-particle band structure may be significantly different from what is deduced within the independent particle model. In the case of cobalt many body effects are even more drastic than an energy renormalization giving rise to a quenching of quasi-particle peaks. Augmenting ab-initio band structure with many-body e-e interactions, we have obtained spin- and k-dependent self-energies, hole spectral functions and quasi-particle energies to be compared with photoemission spectra; our results show that e-e correlations are responsible for strong spin-dependent energy renormalizations.

2004 - Structure optimization effects on the electronic and vibrational properties of Bi2Sr2CaCu2O8 [Articolo su rivista]
Bellini, V; Manghi, Franca; Thonhauser, T; Ambrosch Draxl, C.
abstract

We have studied the effect of structure optimization on the topology of the Fermi surface and on the Raman-active phonons of Bi2Sr2CaCu2O8. By total energy and force minimizations within the density-functional theory we have identified the most stable atomic geometry considering both an idealized body-centered tetragonal structure, inclusive of surface truncation, and a root2xroot2 orthorhombic cell simulating the observed distortions in the BiO planes. The optimization of the tetragonal cell leads to small but visible changes in the topology of the Fermi surface, rounding the shape of the CuO2 barrels, while the orthorhombic distortion is responsible for the umklapp bands that have been observed by angle-resolved photoemission spectroscopy. The latter also gives rise to Raman-active vibrations not permitted in the tetragonal cell and strongly influences the attribution of the phonon peaks measured by experiments.

2003 - Ab initio Fermi surface and conduction-band calculations in oxygen-reduced MoO3 [Articolo su rivista]
Rozzi, C. A.; Manghi, Franca; F., Parmigiani
abstract

This article reports ab initio Fermi surfaces and conduction-band calculations of both stoichiometric and oxygen-reduced MoO3. The data, based on a TB-LMTO approach in LDA, provide a convincing and detailed interpretation of the one-electron removal XPS valence bands, where a clear energy gap is observed for the stoichiometric samples, whereas a significant emission at the Fermi edge is measured for the oxygen reduced system. In addition, the electrical conductivity, as deduced from the shape of the calculated Fermi surface, is confined in the xz plane of the crystal, as required for Luttinger-liquid behavior. These results, when compared to the conduction mechanism observed in the blue bronze K0.3MoO3, clearly suggest that oxygen reduction and doping can bring to very different processes for the electronic transport.

2003 - First principles study of the normal state electronic properties of the Bi-2212 cuprate superconductor [Articolo su rivista]
V., Bellini; C., AMBROSCH DRAXL; Manghi, Franca
abstract

We present detailed first-principles calculations of the normal state electronic properties of the Bi2Sr2CaCu2O8 (Bi-2212) high T-C superconductor by means of the linearized augmented plane wave (LAPW) method within the framework of density functional theory (DFT). We describe the crystal structure by the body-centered tetragonal (BCT) cell with space group I4/mmm and optimize its volume, c/a ratio and atomic positions by total energy and atomic-force minimization. The optimization of the cell leads to small but visible changes in the topology of the Fermi surface, rounding the shape of the CuO2 barrels, and moving both the BiO bands, responsible for the pockets near the (M) over bar point, below the Fermi level. We have then studied the influence of the large distortions in the BiO plane observed in nature by means of an root2 x root2 orthorhombic cell (with Bbmb space group). Differently to what has been observed in the literature for the Bi-2201 compound, we find that for Bi-2212 the orthorhombic distortion does not induce relevant changes to the binding energies of the BiO bands, conserving their metallic character. (C) 2003 Elsevier B.V. All rights reserved.

2003 - Molecular phases in vertically coupled quantum dot molecules [Relazione in Atti di Convegno]
S., Amaha; M., Rontani; Manghi, Franca; Molinari, Elisa; D. G., Austing; K., Ono; S., Tarucha
abstract

We present excitation energy spectra of few-electron vertically coupled quantum dots for strong and intermediate interdot coupling. By applying a magnetic field, we induce ground state transitions and identify the corresponding quantum numbers by comparison with few-body calculations. In addition to atomiclike states, we find novel "molecularlike" phases. The isospin index characterizes the nature of the bond of the artificial molecule and this we control. Like spin in a single quantum dot, transitions in isospin leading to full polarization are observed with increasing magnetic field.

2002 - Quenching of majority-channel quasiparticle excitations in cobalt [Articolo su rivista]
Monastra, S; Manghi, Franca; Rozzi, Ca; Arcangeli, C; Wetli, E; Neff, Hj; Greber, T; Osterwalder, J.
abstract

The low-energy electronic excitations in cobalt are studied by a theoretical method that includes many-body effects and a realistic description of the band structure. Angle-resolved photoemission spectra measured on a thick film of hexagonal close-packed Co on Cu(111) agree well with calculated spectral functions. Because of many-body effects no sharp quasiparticle peaks exist for binding energies larger than 2 eV and in this energy region the spectrum is essentially incoherent. The many-body corrections are much stronger in the majority-spin channel and drastically affect the spin polarization of the spectra.

2002 - Raman Signatures of Classical and Quantum Phases in Coupled Dots: a Theoretical Prediction [Articolo su rivista]
Rontani, Massimo; Goldoni, Guido; Manghi, Franca; Molinari, Elisa
abstract

We study electron molecules in realistic vertically coupled quantum dots in a strong magnetic field. Computing the energy spectrum, pair correlation functions, and dynamical form factor as a function of inter-dot coupling via diagonalization of the many-body Hamiltonian, we identify structural transitions between different phases, some of which do not have a classical counterpart. The calculated Raman cross-section shows how such phases can be experimentally singled out.

2002 - The effect of dielectric polarization-induced surface states on many-body configurations in a quantum dot [Articolo su rivista]
Orlandi, A; Goldoni, Guido; Manghi, Franca; Molinari, Elisa
abstract

We compute the exact lowest energy states and addition spectra for N interacting carriers in semiconductor quantum dots (QDs) embedded in low-dielectric-constant matrices. In particular we focus on the transition between the low dielectric mismatch regime, where single-particle states are confined inside the QD, and the large mismatch regime, where surface localized states may be induced by the dielectric potential outside the QD. In this transition, many-body ground-state reconstructions occur which give rise to strong deviations from the regular shell-filling behaviour dictated by Hand's rules. Our calculated addition spectra indicate that such effects could be monitored in transport experiments.

2001 - Role of electron-electron correlation in the valence states of YBa2Cu3O7: Low-energy excitations and Fermi surface [Articolo su rivista]
Monastra, S; Manghi, Franca; Ambrosch Draxl, C.
abstract

We have studied the role of on-site correlation in the low-energy excitations of YBa2Cu3O7 in the normal state, calculating self-energies and spectral functions according to the three-body-scattering approach. The method allows to include all the details of realistic ab initio band-structure calculations and to augment them with the inclusion of electron-electron correlations, getting quasiparticle energies for one-particle removal. It is found that correlation effects modify the energy dispersion of hole quasiparticle states, both in the high and low binding energy region, and strongly modify the Fermi surface topology.

2001 - Single-electron charging in quantum dots with large dielectric mismatch [Articolo su rivista]
A., Orlandi; M., Rontani; Goldoni, Guido; Manghi, Franca; Molinari, Elisa
abstract

Semiconductor quantum dots characterized by a strong dielectric mismatch with their environment arestudied theoretically through direct diagonalization of the many-body Hamiltonian. The enhancement of theelectron-electron Coulomb interaction, arising from polarization effects, is found to induce a strong increase inaddition energies with increasing dielectric mismatch. For large dielectric mismatch, the excited many-bodystates can undergo reconstructions as the dot is filled with carriers even in the absence of external magneticfields.

2000 - Band-structure effects in the core-level photoemission spectra of NiO [Articolo su rivista]
Rozzi, Ca; Manghi, Franca; Arcangeli, C.
abstract

Calculation of Ni 2p photoelectron spectra for NiO has been performed within a picture which takes into full account the itinerant character of valence electrons and the localized many-body interaction between core and valence electrons. The results of an nb initio band-structure calculation are used as an input for the calculation of self-energy correction and spectral function according to a three-body scattering solution of a many-body Hamiltonian which includes the Coulomb repulsion between core and valence states. The calculated spectrum shows, in agreement with experimental data, a doubly peaked main line which can be attributed to two independent relaxation processes involving valence-baud Ni d states of either pure or hybridized orbital character.

2000 - Enhancement of Coulomb interactions in semiconductor nanostructures by dielectric confinement [Articolo su rivista]
Goldoni, Guido; F., Rossi; A., Orlandi; M., Rontani; Manghi, Franca; Molinari, Elisa
abstract

We present a theoretical analysis of the effect of dielectric confinement on the Coulomb interaction in dielectrically modulated quantum structures. We discuss the implications of the strong enhancement of the electron-hole and electron-electron coupling for two specific examples: (i) GaAs-based quantum wires with remote oxide barriers, where combined quantum and dielectric confinements are predicted to lead to room temperature exciton binding, and (ii) semiconductor quantum dots in colloidal environments, when the addition spectra are predicted to depend on the dielectric mismatch. (C) 2000 Elsevier Science B.V. All rights reserved.

1999 - Correlation effects in the low energy region of nickel photoemission spectra [Articolo su rivista]
Manghi, Franca; V., Bellini; J., Osterwalder; T. J., Kreutz; P., Aebi; C., Arcangeli
abstract

The role of on-site correlation in the low-energy excitations of nickel is studied by comparing the results of high-angular and high-energy resolution photoemission spectroscopy with quasiparticle states calculated as a three-body scattering solution of a multiorbital Hubbard model. It is found that correlation effects modify the energy dispersion and spin polarization of electron states and are essential in order to get a quantitative agreement with experimental data.

1999 - Coulomb Correlation in the Addition Spectra of Single and Coupled Quantum Dots [Relazione in Atti di Convegno]
M., Rontani; F., Rossi; Manghi, Franca; Molinari, Elisa
abstract

Quantum dots

1999 - Coulomb correlation effects in semiconductor quantum dots: The role of dimensionality [Articolo su rivista]
Rontani, M; Rossi, F; Manghi, Franca; Molinari, Elisa
abstract

We study the energy spectra of small three-dimensional (3D) and two-dimensional (2D) semiconductor quantum dots through different theoretical approaches (single-site Hubbard and Hartree-Fock Hamiltonians); in the smallest dots we also compare with exact results. We find that purely 2D models often lead to an inadequate description of the Coulomb interaction existing in realistic Structures, as a consequence: of the overestimated carrier localization. We show that the dimensionality of the dots has a crucial impact on (i) the accuracy of the predicted addition spectra, and (ii) the range of validity of approximate theoretical schemes. When applied to realistic 3D geometries, the latter are found to be much more accurate than in the corresponding 2D cases for a large class of quantum dots; the single-site Hubbard Hamiltonian is shown to provide a very effective and accurate scheme to describe quantum dot spectra, leading to good agreement with experiments. [S0163-1829(99)10211-X].

1999 - Multiple quantum phases in artificial double-dot molecules [Articolo su rivista]
M., Rontani; F., Rossi; Manghi, Franca; Molinari, Elisa
abstract

We study coupled semiconductor quantum dots theoretically through a generalized Hubbard approach, where intra- and inter-dot Coulomb correlation, as well as tunneling effects are described on the basis of realistic electron wavefunctions. We find that the ground-state configuration of vertically coupled double dots undergoes non-trivial quantum transitions as a function of the inter-dot distance d; at intermediate values of d we predict a new phase that should be observable in the addition spectra and in the magnetization changes. (C) 1999 Elsevier Science Ltd. All rights reserved.

1999 - Theory of addition spectra in double quantum dots: Single-particle tunneling vs Coulomb interactions [Articolo su rivista]
M., Rontani; F., Rossi; Manghi, Franca; Molinari, Elisa
abstract

We study coupled semiconductor quantum dots theoretically using a generalized Hubbard approach, where intra- and inter-dot Coulomb correlation, as well as tunneling effects are described on the basis of realistic electron wavefunctions. We find that the ground-state configuration of vertically coupled double dots undergoes non-trivial quantum transitions as the inter-dot distance d changes; at intermediate values of d we predict a new phase that should be observable in the addition spectra and in the magnetization changes.

1998 - Addition energies in semiconductor quantum dots: Role of electron-electron interaction [Articolo su rivista]
M., Rontani; F., Rossi; Manghi, Franca; Molinari, Elisa
abstract

We show that the addition spectra of semiconductor quantum dots in the presence of magnetic field can be studied through a theoretical scheme that allows an accurate and practical treatment of the single-particle states and electron-electron interaction up to large numbers of electrons. The calculated addition spectra exhibit the typical structures of Hund-like shell filling, and account for recent experimental findings. A full three-dimensional description of Coulomb interaction is found to be essential for predicting the conductance characteristics of few-electron semiconductor structures.

1998 - On-site correlations in narrow band materials [Relazione in Atti di Convegno]
Manghi, Franca; V., Bellini; M., Rontani; C., Arcangeli
abstract

We present the results of a recently developed approach where the interplay between the itinerant and localized character of electrons in narrow band materials is described by adding on-site correlations to a realistic band calculation

1997 - La Transizione da Piano a Mercato E il Modello Ising [Working paper]
Caselli, Gian Paolo; Manghi, Franca
abstract

1997 - Localized and itinerant character of electron states in the photoemission from CuGeO3 [Articolo su rivista]
Villafiorita, A; Manghi, Franca; Parmigiani, F; CALANDRA BUONAURA, Carlo
abstract

It is shown that electron correlation among Cu d-electrons explains the photoemission data of CuGeO3 and is responsible for the insulating behaviour and of the observed complex satellite structures. The analysis and interpretation of the experiments require the use of a multi-band Hamiltonian which explicitly includes both on site electron correlation and a detailed description of the single-particle band states.

1997 - On-site correlation in valence and core states of ferromagnetic nickel [Articolo su rivista]
Manghi, Franca; Bellini, V; Arcangeli, C.
abstract

We present a method which allows us to include narrow-band correlation effects in the description of both valence and core states and we apply it to the prototypical case of nickel. The results of an ab initio band calculation are used as input mean-field eigenstates for the calculation of self-energy corrections and spectral functions according to a three-body scattering solution of a multiorbital Hubbard Hamiltonian. The calculated quasiparticle spectra show a remarkable agreement with photoemission data in terms of bandwidth, exchange splitting, satellite energy position of valence states, and spin polarization of both the main line and the satellite of the 3p core level.

1996 - Structural and electronic properties of Sb islands on GaAs (110) [Articolo su rivista]
Magri, Rita; Manghi, Franca; CALANDRA BUONAURA, Carlo
abstract

We present the results of theoretical calculations of the electronic structure of the Sb/GaAs(110) interface in the submonolayer coverage regime performed in the full ab initio self-consistent pseudopotential scheme. Different structural models for the edges of the extended Sb islands have been considered and their equilibrium geometry has been determined by total energy minimization. The single particle band structure shows interface states arising mainly from the incomplete bonding of the Sb adatoms at the terrace edge to the substrate, which fall within the optical gap. Distinct features are associated to different island terminations. The interface turns out to be metallic in all the considered cases with a partially occupied peak at the Fermi level. We have also studied the effect of including explicitly the on-site Hubbard electron-electron correlation in the calculation of the quasiparticle spectrum, obtaining the observed semiconducting interface when the Coulomb interaction parameter U is larger than 3 eV. The interface states within the optical band gap can be present also at higher coverages when some disorder exists, evidentiating a general mechanism for the Fermi level pinning at this interface.

1995 - Progress in computational physics of matter: methods, software and applications [Monografia/Trattato scientifico]
Reatto, L.; Manghi, Franca
abstract

The understanding of the microscopic processes occurring in solids and liquids is a significant challange in computational physics. The rapid growth of computer power including the new paralell architectures has stimulated a ferment of new theoretical and computational ideas.

1994 - Electron electron correlation for Sb on GaAs(110) [Relazione in Atti di Convegno]
Magri, Rita; Manghi, Franca; CALANDRA BUONAURA, Carlo
abstract

We have studied the effect of including the on-site Hubbard electron-electron correlation in the calculation of the quasiparticle spectrum, obtaining the observed semiconducting interface when the Coulombinteraction parameter U is larger than 3 eV. The interface states within the optical band gap can bepresent also at higher coverages when some disorder exists, evidentiating a general mechanism forthe Fermi level pinning at this interface.

1994 - Physics of Solid Surfaces: Electronic and Vibrational Properties [Monografia/Trattato scientifico]
CALANDRA BUONAURA, Carlo; Chiarotti, G.; Gradmann, U.; Jacobi, K.; Manghi, Franca; Maradudin, A. A.; Tong, S. Y.; Wallis, R. F.
abstract

n the last two decades surface physics has experienced an explosive expansion caused by the development and/or substantial improvement of surface sensitive techniques and UHV appa-ratus. It has grown into a mature field of research, with data of the highest accuracy and repro-ducibility. Surface physics is of great importance for technological applications like control of the work function of semiconductors,interface physics,field effect devices, molecular beam epitaxy, chemisorption and catalysis, corrosion, surface hardening etc.. The present volume is restricted to the so-called "clean" surfaces, i.e. to surfaces atomically clean and well characterized,leaving the more complex field of the contaminated surfaces and overlayers to a later occasion.

1994 - Quasi-particle band structure of NiO: The Mott-Hubbard picture regained [Articolo su rivista]
Manghi, Franca; CALANDRA BUONAURA, Carlo; Ossicini, Stefano
abstract

We demonstrate that the Hubbard correlation among Ni 3d electrons is able to reproduce the insulating character of NiO, the correct value of the gap, the orbital character of the valence band edge, and the presence of satellite structures. We have determined the quasiparticle spectra starting from the complex single particle band structure of NiO and including the on-site Hubbard repulsion according to a recently developed three-body scattering theory which allows us to treat highly correlated and highly hybridized systems. The calculated quasiparticle band structure is in excellent agreement with photoemission data.

1994 - SURFACE TERMINATION OF YBA2CU3O7-X SYSTEMS [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

Owing to the complexity of their structure, YBa2Cu3O7-x systems can have several different terminations of the crystal. Even considering basal plane surfaces only, six possible terminations are found for an ideal truncation of the crystal, having different electronic properties. The characterization of the real surfaces produced by fracturing sintered materials, by cleaving a mono-crystal or by growing a thin film is a very difficult task, due to the occurrence of processes such as contaminant segregation, oxygen loss from the external planes and surface reconstruction. Here we review the experimental work on this subject and critically compare the outcomes of different spectroscopical experiments. The data are discussed in the light of the available theoretical results for the surface band structure of the ideal basal plane surfaces. The role of the surface in determining a non-superconducting surface phase is illustrated. Possible morphological and structural models for the observed surfaces are presented.

1994 - Three-Body Scattering Theory of Correlated Hole and Electron States [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We describe a theoretical scheme for the determination of quasiparticle spectra starting from the energy band structure of a metal and treating the on-site Hubbard repulsion beyond the mean-field theory. The method relies upon an expansion of the many-body states in terms of uncorrelated states with a different number of electron-hole pairs. By truncating the expansion to include configurations with one or two pairs one can achieve approximate expressions of the electron and hole self-energies. The interparticle scattering matrices appearing in such expressions are conveniently calculated using the Faddeev approach. Calculations performed for a constant density of states allow us to illustrate the role of three-body correlations in the metal-insulator transitions.

1992 - ANION-SPECIFIC SURFACE VALENCE-BAND STATES IN HETEROPOLAR SEMICONDUCTORS - THE CASE OF GAP(110) AND INP(110) [Articolo su rivista]
SANCROTTI, M; DUO, L; CALLIARI, L; MANGHI, Franca; COSSO, R; WEIGHTMAN, P.
abstract

The surface- and anion-specific valence-band states of heteropolar P containing III-V semiconductors [GaP(110) and InP(110)] have been determined by analysis of the Auger P L2,3 VV line shape of the ascleaved samples and the well-ordered epitaxial Sb-covered interfaces. The experimental spectra are analyzed in terms of slab-resolved partial density-of-states calculations performed for different surface structural models.

1992 - BASAL-PLANE SURFACES OF YBA2CU3O7 - SINGLE-PARTICLE RESULTS AND VALENCE-BAND SPECTRA [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Minerva, Tommaso
abstract

YBa2Cu3O7 has a complex structure, which allows for six different basal-plane surfaces. For each of them we have calculated the local density of states in the outermost crystal layers using a tight-binding method, and found that surface states with dangling-bond character are present. The surfaces obtained by cutting the bond between in-plane copper ions and axial oxygen atoms appear to be electrostatically stable, the charge distribution in the outermost planes closely resembling the bulk one. Their surface band structures show dangling-bond states with significant dispersion, which are proposed to be responsible for the surface feature observed by angle-resolved photoemission. By using a model Hamiltonian that includes correlation effects, we have calculated the hole self-energy and determined the valence-band satellite distribution for different crystal terminations and compositions. The results show that satellites are significantly affected by the surface conditions. It is concluded that the role of the surface is crucial in modeling the photoemission spectra.

1992 - ELECTRONIC STATES AT THE (111) SURFACE OF NI DISILICIDE [Articolo su rivista]
Manghi, Franca; G., Guidetti; Bisi, Olmes
abstract

The electronic structure of the NiSi2(111) surface has been calculated in the tight-binding scheme using an accurate parametrization of first-principles results for the bulk system. Two surface terminations are considered which correspond to two possible surface phases. The resulting surface band structures are quite different in the two cases suggesting a possible spectroscopical characterization of the surface geometry.

1992 - EXPERIMENTAL AND THEORETICAL SURFACE COMPONENT OF THE PL2,3VV AUGER LINESHAPE IN GAP(110) - THE USE OF ORDERED (1X1) SB OVERLAYERS [Articolo su rivista]
Duo, L; Sancrotti, M; Cosso, R; Weightman, P; Manghi, Franca
abstract

An analysis of the theoretical and experimental surface contribution of the PL2,3VV Auger lineshape in GaP(110) is performed. From the theoretical point of view the lineshapes are calculated within a single-particle framework from a slab-by-slab tight-binding calculation of the ideal and real relaxed surfaces. The experimental information is extracted by comparing the Auger feature of as-cleaved GaP(110) and of the GaP(110) interfaced with one ordered monolayer of Sb. This allows the LVV surface component to be isolated. A comparison with theory, showing strong similarities in the position of the surface-related features is discussed.

1992 - OVERLAYER-INDUCED AUGER LINE-SHAPE CHANGES - THE CASE OF THE P L2,3 VV TRANSITION AT THE INP(110)/SB INTERFACE [Articolo su rivista]
Calliari, L; Sancrotti, M; Duo, L; Cosso, R; Weightman, P; Manghi, Franca
abstract

A joint experimental and theoretical investigation of the PL2,3VV spectrum from the InP(110) surface is presented. The aim is to check for the possibility of separately measuring its surface and bulk components. It is shown that non-reactive overlayers, such as Sb in this case, can be successfully exploited to this end. The comparison with computed spectra allows us to finally present the measured surface component of the PL2,3VV spectrum from InP(110).

1992 - QUENCHING THE SURFACE ELECTRONIC-STRUCTURE OF P-CONTAINING-III-V SEMICONDUCTORS VIA ORDERED (1X1) SB OVERLAYERS - A PL2,3VV AUGER LINE-SHAPE ANALYSIS [Articolo su rivista]
Sancrotti, M; Duo, L; Calliari, L; Marchetti, F; Cosso, R; Weightman, P; Manghi, Franca
abstract

We report experimental PL2,3VV Auger line shapes of as-cleaved GaP(110) and InP(110) surfaces and of the relative Sb p(1 x 1) interfaces along with calculated slab-resolved densities of states (DOS). The joint experimental and theoretical analysis allows us to disentangle the surface-specific PL2,3VV contribution from the total signal of the as-cleaved surfaces.

1992 - RESOLVING THE SURFACE CONTRIBUTION OF THE P L2, 3 VV AUGER LINESHAPE OF GAP(110) VIA USE OF (1 X-1) SB OVERLAYERS [Articolo su rivista]
Duo, L; Sancrotti, M; Cosso, R; Weightman, P; Manghi, Franca
abstract

An experimental and theoretical study of the band-like P L2,3VV Auger lineshape for GaP(110) is reported (kinetic energy almost-equal-to 120eV). By deposition of one monolayer of Sb (isoelectronic to P) we determine the surface-related Auger lineshape as the difference between the two spectra measured from the as-cleaved surface and the GaP/Sb interface. Theoretical calculations based on a single particle approach including different structural coordination models (i.e. ideally truncated surface, real relaxed surface, ordered Sb overlayer) are performed, which allows to isolate the surface contribution of the L2,3VV Auger profile from the bulk related lineshape. Moreover the results of the joint analysis are discussed giving excellent agreement between calculations and measurements and pointing toward an interpretation of the P LVV lineshape in terms of surface structural probe.

1992 - SURFACE LOCAL DENSITY OF STATES OF INP(110) VIA PL2,3VV AUGER LINESHAPE - THE ROLE OF AN ORDERED (1X1) SB OVERLAYER [Articolo su rivista]
Calliari, L; Marchetti, F; Sancrotti, M; Duo, L; Cosso, R; Weightman, P; Manghi, Franca
abstract

An experimental and theoretical investigation on the PL2,3VV Auger lineshape of the InP(110) surface is presented. A band-like picture provides a good description of the spectral features. In addition, deposition of one monolayer of Sb on InP(110) is shown to drive the surface atoms into an environment similar to that present in the bulk, so that a comparison between the PL2,3VV spectrum from the clean and Sb-covered sample allows us to discriminate between the surface contribution and the bulk contribution to this surface-sensitive Auger transition.

1991 - SATELLITES FROM HYBRIDIZED CU-O STATES IN YBA2CU3O7 [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Minerva, Tommaso
abstract

The satellite structure of YBa2Cu3O7 compound is calculated starting from an accurate description of the bulk band structure and evaluating the self-energy effects arising from the intra-atomic Coulomb repulsion on the copper and oxygen sites. A continuum of satellites of d8 character originating from the highly hybridized Cu-O bands is found between 8 and 13 eV binding energy. Comparison with the experimental data allows one to explain the behavior of the Cu satellites in resonant photoemission and provides indications about the intrinsic character of the satellite at 9 eV.

1991 - Surface local field effect in the optical properties of GaAs(110) and GaP(110), [Articolo su rivista]
C. M., Wijers; R., Del Sole; MANGHI, Franca
abstract

A method for the calculation of the surface local-field effect on reflectance has been developed. It also takes into account the different polarizabilities of surface and bulk. Application has been made to GaAs(110) and GaP(110), starting from first-principles one-electron calculations of surface optical properties. The inclusion of local fields has important—yet not drastic—effects on line shapes of reflectance-anisotropy and differential-reflectivity measurements.

1990 - ANISOTROPY IN THE OPTICAL-SPECTRUM OF THE GAAS(110) SURFACE [Articolo su rivista]
Manghi, Franca; Molinari, Elisa; Selloni, A; Delsole, R.
abstract

A Comment on the Letter by X. Zhu et al., Phys. Rev. Lett. 63, 2112 (1989).

1990 - ANISOTROPY OF SURFACE OPTICAL-PROPERTIES FROM 1ST-PRINCIPLES CALCULATIONS [Articolo su rivista]
Manghi, Franca; Delsole, R; Selloni, A; Molinari, Elisa
abstract

The optical properties of GaAs(110) and GaP(110) surfaces are studied by means of self-consistent local-density calculations. A very large contribution to the reflectance anisotropy is found to be related to transitions which do not involve surface states. These transitions give a substantial—yet smaller—contribution also to the differential reflectivity. Comparison is made with relevant experimental data.

1990 - Experimental and theoretical evidence of image states at semiconductor surfaces: the case of GaP(110) [Articolo su rivista]
Manghi, Franca; P., Perfetti; B., Reihl
abstract

The first theoretical and experimental analysis of image states at a semiconductor surface is presented: results of angle resolved inverse photoemission and of ab-initio pseudopotential calculation in the non-local density approximation for GaP(1 1 0) are compared showing the presence of a well defined image state with a dispersion in k-space very different from the one predicted by simple models

1990 - OXYGEN-INDUCED SURFACE-STATES IN YBA2CU3O7 [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Minerva, Tommaso
abstract

We present the results of theoretical calculations of the surface electronic structure of YBa2Cu3C7 assuming different crystal terminations. Through a detailed analysis of the distribution of the valence charge near the surface we show that hole distribution may be significantly modified at the surface, due to the band narrowing and to the presence of surface states. The role of these modifications in determining the shape of the one-hole spectra is discussed.

1990 - THEORETICAL INVESTIGATION OF THE FERMI LEVEL PINNING AT THE SB-GAAS(110) INTERFACE [Articolo su rivista]
Manghi, Franca; CALANDRA BUONAURA, Carlo
abstract

We present the results of theoretical calculation of the electronic structure of the Sb-GaAs(110) interface in the submonolayer coverages perormed in the semiempirical TB scheme. Iterface states arising from the incomplete bonding of Sb atoms to the substarte apepar in the band gap; such states can be prsent also at higher coverages when some disorder exists, evidentiating a general mechanism for fermi lev pinning at the interface

1990 - Theoretical interpretation of valence band photoemission spectra in YBa2Cu3O7 [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Minerva, Tommaso
abstract

Angle resolved one-hole spectra have been calculated starting from a realistic tight-binding Hamiltonian and including correlation and surface effects. The hole self-energy has been evaluated using the t-matrix approximation for the hole-hole scattering. To account for surface effects the local density of states of the outermost atomic layers has been determined assuming an ideal termination of the crystal and a non polar basal plane surface. The theoretical curves allow one to assign the main features of the spectra at high symmetry points of the Brillouin zone, except for the peak observed at 8.5 eV binding energy. It is suggested that the discrepency may arise from the neglecting of the k-dependence in the self-energy or from the extrinsic nature of the peak.

1989 - 1ST-PRINCIPLES CALCULATION OF ANISOTROPIC REFLECTANCE AT THE GAAS(110) SURFACE [Articolo su rivista]
Manghi, Franca; R., Delsole; Molinari, Elisa; A., Selloni
abstract

The optical properties of the GaAs(110) surface are studied by means of self-consistent local-density slab calculations. It is found that a large contribution to the calculated anisotropy of the clean surface reflectance is related to transitions which do not involve surface states. Comparison is made with differential reflectivity and reflectance anisotropy experiments.

1989 - GIANT QUASI-PARTICLE SHIFTS OF SEMICONDUCTOR SURFACE-STATES [Articolo su rivista]
Bechstedt, F; Delsole, R; Manghi, Franca
abstract

The differences between the energy positions of surface bands in quasi-particle and local-density approximations are calculated taking into account the different screening properties of a semiconductor and of an electron gas of the same average density. Gap corrections of the order of 1.5 eV are computed for GaP(110) and GaAs(110) surfaces, in good agreement with experiment.

1989 - One hole spectra at YBa2Cu3O7 surfaces [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Minerva, Tommaso
abstract

We present a theoretical study of the modification of the one-hole spectra induced by the surface in YBa2Cu3O7. Basal plane surfaces terminated either with Ba or CuO planes are considered. Correlation effects are included by using a Hubbard model hamiltonian and by calculating the self-energy in the low density approximation. The results indicate that both the main bands and the satellites are sensitive to the choice of the surface.

1989 - Origin of surface anisotropies in the optical spectra of III-V compounds [Articolo su rivista]
Manghi, Franca; Molinari, Elisa; R., Del Sole; A., Selloni
abstract

We present results of ab initio calculations of optical spectra of GaP and GaAs (110) surfaces, and show that transitions between bulk single-particle states modified by the crystal truncation account for the largest contribution to above-gap optical anisotropy of these systems.

1989 - SURFACE STOICHIOMETRY AND VALENCE ELECTRONIC-STRUCTURE OF YBA2CU3O7-X [Articolo su rivista]
F., Parmigiani; G., Samoggia; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We report x-ray photoemission data from YBa2Cu3O7−x showing that the measured composition and the electronic structure changes significantly upon the photoelectron escape depth. For large take-off angles the valence band spectrum near the Fermi edge is well structured and shows a number of features arising from Cu-O hybrid states. Their intensities are drastically reduced in the energy distribution curves measured at grazing angles. These results are interpreted assuming that the surface is mainly composed by Ba-O planes. This interpretation is shown to be consistent with electronic structure calculations for the bulk and for a YBa2Cu3O7−x surface terminated with a Ba plane and produced by cutting the Cu2 O4 bond normal to the c axis. The local density of states calculated on this basis and taking into account electron correlation effects is shown to be consistent with many significant behaviors experimentally observed in the YBa2Cu3O7−x valence band. Journal of Applied Physics is copyrighted by The American Institute of Physics.

1989 - Surface effects in the electronic properties of YBa2Cu3O7 [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Goldoni, Guido; Manghi, Franca; Magri, Rita
abstract

The electronic structure of basal plane surfaces of the high-T, superconducting material YBa,Cu,O, has been determined using a tint-binding Hamilto~~n derived from a first-p~nciple calculation of the bulk phase. The surface local density of states has been obtained for four different surface configurations, which differ for the yttrium and oxygen content. The results show that the presence and state of the surface have a strong influence on the distribution of single particle states. The nature of the surface induced modifications is detailed and the relevance of the results to the understanding of experimental data is shortly discussed.

1989 - Surface effects on the electronic properties of YBa2Cu3O7 [Articolo su rivista]
C., Calandra; Manghi, Franca; Minerva, Tommaso; Goldoni, Guido
abstract

We present the results of a theoretical study of the modifications induced by the surface on the electronic structure of YBa2Cu3O7. Basal plane surfaces terminated with Ba and with Cu-O planes are considered. The calculated local densities of states show that the main structures of the bulk density of states may be drastically modified, specially near the Fermi energy, and new surface derived features appear in the spectrum. Significant changes occur also in the occupancies of the atoms near the surface.

1987 - Bonding and surface electronic structure of an Sb overlayer on GaP(110) [Articolo su rivista]
Manghi, Franca; CALANDRA BUONAURA, Carlo; Molinari, Elisa
abstract

We calculate the electronicstructure of an Sboverlayer on GaP(110) using a self-consistent pseudopotential approach. A detailed analysis of the energy position and the orbital nature of the overlayer induced states shows that the main contribution to the bonding between the adatoms and the substrate comes from states around 4 eV below the valence band maximum. A model description of the outcomes of the full calculation is presented, which differs from previous interpretations.

1987 - Microscopic calculation of differential reflectivity of GaP(110) [Articolo su rivista]
Manghi, Franca; Molinari, Elisa; R., del Sole; A., Selloni
abstract

We compute the optical properties of semiconductor surfaces starting from the self-consistent electronic structures determined using local pseudopotentials with a plane-wave basis set. Calculations for a 9 layer (110) slab of GaP are carried out with both clean and H covered surfaces. Differential reflectivity spectra and their anisotropies are interpreted in terms of transitions involving surface states.

1986 - Non-local exchange and correlation in surface calculation: an application to GaAs(110) [Articolo su rivista]
Manghi, Franca
abstract

The self-consistent pseudopotential method has been applied to the determination of the electronic structure of the GaAs(110) surface in the framework of the Kohn-Sham density-functional theory, using the nonlocal exchange-correlation energy functional of Gunnarsson and Jones. It is shown that the inclusion of nonlocality in the description of the exchange-correlation energy does not change surface-state energies significantly. The behavior of the charge density and of the potential outside the surface and some measurable properties related to them, such as the corrugation parameters, is calculated and discussed.

1985 - Band structure calculation for GaAs and Si beyond the local density approximation [Articolo su rivista]
Manghi, Franca; G., Riegler; Bertoni, Carlo Maria; G. B., Bachelet
abstract

We have performed pseudopotential self-consistent band-structure calculations for bulk solids in the framework of the Kohn-Sham density-functional theory, applying the nonlocal exchange-correlation functional of Gunnarsson and Jones to valence electrons with no further approximation. We present our method together with representative results for GaAs and Si, the main interest being focused on single-particle energy eigenvalues and gaps. An accurate comparison of the results obtained with this approach and the local-density-approximation results is given. The dependence of such a comparison on the choice of the basis set (localized Gaussian orbitals or plane waves) is also examined, and found to be unimportant. The reliability of the method, the changes in band structure, their k→ dependence, and the behavior of the exchange-correlation potential throughout the unit cell are discussed. We find that the inclusion of nonlocality in the description of exchange and correlation does not change valence-band states significantly and increases by a very small amount the energy difference between some conduction-band states and the top of the valence band. The increase (≲0.2 eV) is, however, insufficient to solve the problem of the local-density-approximation minimum band gaps, which remain much smaller than the measured energy gaps.

1985 - Theoretical study of the electronic structure of the GaP-Si(110) interface [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Bertoni, Carlo Maria
abstract

Self-consistent pseudopotential calculations have been performed to determine the electronicstructure of a Si overlayer on GaP(110) surface. The results show that both filled and empty Si-induced states appear in the gap. The consequences for the Fermi level pinning are discussed and recent experimental results are explained.

1984 - ELECTRONIC-PROPERTIES OF THE Cs-GaAs(110) INTERFACE AT MONOLAYER COVERAGE [Articolo su rivista]
Manghi, Franca; CALANDRA BUONAURA, Carlo; Bertoni, Carlo Maria; Molinari, Elisa
abstract

The electronic properties of the interface obtained by a monolayer deposition of Cs onto GaAs(110) are studied theoretically by modelling the overlayer with a thin jellium slab of appropriate electron density. The calculations are carried out self-consistently with a pseudopotential approach for two different substrate geometries, corresponding to the ideal and the relaxed configuration of the surface atoms. In both cases a band of Cs-induced states is found in the gap which hybridizes with the dangling and back bond states of the GaAs surface. The change in the work function upon Cs deposition is calculated and found for both the substrate geometries in good agreement with the experimental data. Comparison with electron energy loss and photoemission experiments indicates that the model with the surface in the relaxed configuration is the most appropriate one.

1983 - ELECTRON-STATES AT Zn(0001) SURFACE [Articolo su rivista]
Manghi, Franca; Bertoni, Carlo Maria
abstract

The electronic structure of the Zn(0001) surface is analyzed through a realistic slab calculation with an accurate tight-binding sp-d model hamiltonian. The results are compared with a recent photoemission investigation of this surface. The comparison with noble and near-noble metal surfaces, with reference to the surface states in the s-p gap at the centre of the surface Brillouin zone, is also discussed.

1983 - ELECTRON-STATES OF AN Sb-ORDERED OVERLAYER ON GaAs(110) [Articolo su rivista]
Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca; Molinari, Elisa
abstract

The electronic properties of an Sb overlayer deposited onto a GaAs(110) surface have been calculated using a self-consistent-pseudopotential approach and assuming the ordered-overlayer geometry proposed in recent low-energy electron diffraction studies. The results show that Sb adatoms are bound by strong covalent bonds to the substrate and that various overlayer or chemisorption-induced states appear throughout the valence band. Comparison with photoemission data allows us to assign a major Sb-induced structure appearing in the energy distribution curves.

1983 - NONLOCAL EXCHANGE AND CORRELATION AND SEMICONDUCTOR BAND-STRUCTURE [Articolo su rivista]
Manghi, Franca; G., Riegler; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; G. B., Bachelet
abstract

We present the results of self-consistent band-structure calculations for bulk GaAs, in which the density-functional theory is applied with a nonlocal expression for the exchange and correlation energy, Exc[n(r⃗)]. Using the same ionic potentials and basis set, other local expressions for exchange and correlation are also considered for comparison. It will be shown that the inclusion of nonlocality in the exchange and correlation potential improves the description of the valence bands, but does not solve the "gap problem" experienced by the simpler local expressions (i.e., too small a gap).See AlsoErratum: F. Manghi, G. Riegler, C. M. Bertoni, C. Calandra, and G. B. Bachelet, Erratum: Nonlocal exchange and correlation and semiconductor band structure, Phys. Rev. B 29, 5966 (1984).For revisions.

1982 - Aspects of self-consistent procedures in surface pseudopotential calculations [Articolo su rivista]
Manghi, Franca; Molinari, Elisa
abstract

The authors present a discussion of the main features of self-consistency for clean and chemisorbed surfaces in the local density functional formalism. The technical details of the procedure are analysed together with the behaviour of the various contributions to the surface potential. They show that the iterative approach to self-consistency can be made efficient and quick when the starting potential is properly chosen and the components of the potential more sensitive to the self-consistent process are singled out.

1982 - SELF-CONSISTENT PSEUDOPOTENTIAL CALCULATION OF THE ELECTRONIC-PROPERTIES OF THE INP (110) SURFACE [Articolo su rivista]
Manghi, Franca; Molinari, Elisa; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo
abstract

Self-consistent pseudopotential calculations for InP(110) surface have been carried out using the repeated slab method and assuming relaxed surgace geometry. Various surface states have been found and their character and symmetry properties have been investigated by analyzing the corresponding pseudocharge density maps. Comparison between self-consistent and non-self-consisting calculations shows significant differences.The results are in agreement with the experimental finding obtained by different techniques.

1982 - THEORETICAL INVESTIGATION OF HYDROGEN CHEMISORPTION ON GA-CONTAINING III-V-COMPOUNDS [Articolo su rivista]
Manghi, Franca; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Molinari, Elisa
abstract

A fully self-consistent pseudopotential calculation of the electronic properties of atomic hydrogen chemisobed on GaAs and GaP (110) surface is reported. Different chemisorption geometries ans substrate coverages are considered. The results are compared with the experimental information to select a structural model.

1981 - Copper on Ni(111): the electron states from submonolayer to several monolayer coverages [Articolo su rivista]
Abbati, ; L., Braicovich; A., Fasana; Bertoni, Carlo Maria; Manghi, Franca; CALANDRA BUONAURA, Carlo
abstract

Experimental and theoretical results are presented for Cu on an Ni(111) surface. The monolayer case is discussed in detail in connection with theoretical results of a tight-binding calculation. The theory accounts for the Cu 3d-peak position and the modification of the substrate density of states. Also, the measured Cu 3d line shape can be understood on the basis of the theory.

1981 - EVIDENCE FOR SEMICONDUCTOR-SEMICONDUCTOR INTERFACE STATES - SI(111) (2X1)-GE [Articolo su rivista]
P., Perfetti; N. G., Stoffel; A. D., Katnani; G., Margaritondo; C., Quaresima; F., Patella; A., Savoia; Bertoni, Carlo Maria; Manghi, Franca
abstract

A direct correlation was found for the first time between theory and experiments on the localized electronic states at a semiconductor-semiconductor interface. The investigation involved synchrotron-radiation photoemission experiments and tight-binding calculations on Ge adatoms on cleaved Si substrates. The theoretically predicted interface states in a region 4-9 eV below the Fermi level were detected in the experimental spectra. These occupied states and their unoccupied counterparts have a fundamental influence on the localized one-electron transitions and on relevant heterojunction parameters in transport processes.

1981 - Theoretical study of the electronic structure of GaP(110) [Articolo su rivista]
Manghi, Franca; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Molinari, Elisa
abstract

A self-consistent pseudopotential approach has been used to calculate the electronic structure of GaP(110) surface in both ideal and relaxed configurations. Calculations have been performed using the repeated slab method and a local form of the bare ionic pseudopotential. An efficient self-consistent procedure, which allows us to obtain quick convergence and eliminates some difficulties found in previous applications of the method, has been used. Particular care has been devoted to have complete consistency between bulk and slab calculations. Our results for the ideal surface show various surface states, whose distribution and nature are similar to those found in tight-binding calculations. For the geometry of the relaxed surface we assumed a rotation-relaxation model determined by a recent low-energy electron diffraction study. With this geometry our results show that a nonvanishing density of empty surface states, to a large extent due to backbonds, remains in the gap. The orbital composition of these states, as well as of all the other surface features, is detailed, together with the mirror-plane symmetries relevant in the interpretation of angle-resolved photoemission data. Our results are in agreement with the experimental data provided by various different measurements.

1981 - Two dimensional band structure of chemisorbed chlorine on GaAs(110) [Articolo su rivista]
G., Margaritondo; J. E., Rowe; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

The two-dimensional electronic energy bands of an ordered Cl overlayer on GaAs (110) were mapped by angle-resolved photoemission spectroscopy with synchrotron radiation. The results were compared to bands calculated with an empirical tight-binding approach. This comparison shows that the Cl adatoms are bound to As atoms and that the substrate atoms are relaxed from their positions in a way qualitatively similar to that of clean-surface GaAs (110).

1980 - MICROSCOPIC ASPECTS OF SI-GE HETEROJUNCTION FORMATION [Articolo su rivista]
Nannarone, Stefano; F., Patella; P., Perfetti; C., Quaresima; A., Savoia; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present the results of an investigation of the electronic structure of heterojunctions formed by deposition of Germanium on Si (lll) surfaces. Energy Loss Spectra for various Ge coverages have been taken and compared with theoretical calculations. The results indicate that the interface is abrupt and at low coverages Ge is deposited uniformly on the substrate. Above 2 monolayers coverage modifications in the electronic structure appear probably caused by the growth mechanism.

1979 - CHEMISORPTION GEOMETRY ON CLEAVED III-V SURFACES - CL ON GAAS, GASB, AND INSB [Articolo su rivista]
Margaritondo, G; Rowe, Je; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

Experimental angle-integrated photoemission curves taken on Cl-covered (110) surfaces of GaAs, GaSb, and InSb have been compared to tight-binding calculations of the local density of states. The results clearly demonstrate that the Cl adatoms are bound to the anion substrate atoms rather than to the cation substrate atoms. Some qualitative information is also provided on surface relaxation and on chemisorption bond lengths.

1979 - Chemisorption geometry on cleaved GaAs (110) surfaces [Relazione in Atti di Convegno]
G., Margaritondo; J. e., Rowe; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

An experimental and theoretical study of Cl chemisorption on GaAs(110) shows that adatoms are bound to surface As atoms

1979 - Surface electron states at the (110) surfaces of III-V semiconductors [Relazione in Atti di Convegno]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present a theoretical investigation of the effect of surface relaxation on the electronic structure of the cleavage faces of III-V compounds. The energy position of the surface states, their localization and orbital composition are discussed.

1978 - A theoretical study of ordered monolayer films of Copper [Relazione in Atti di Convegno]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

The aim of this communication is to present some new results of a theoretical study of the density of states of ultra-thin metallic copper films deposited on metal substrates and to compare them with the experimental information. Our results for Cu on Zn(0001) and for Cu on Ni(111) shows that strong modifications can occur in the electronic structure of the overlayer with respect to the isolated monolayer case.

1978 - Electronic Structure of an Ordered Monolayer of Cu on Zn(0001) [Articolo su rivista]
I., Abbati; L., Braicovich; Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We have measured the energy distribution curves of photoelectrons (hν=21.2 eV) from a Zn single-crystal (0001) face covered by an ordered Cu monolayer and from bulk Cu. We have found a narrow (2.3-eV total width) Cu d-state peak 1.20 eV below the position of the peak of bulk Cu 3d structure. We have also calculated the density of states for both a Cu monolayer on Zn and an unsupported Cu monolayer. Theory is in good agreement with experiments. The overlayer density of states is shown to be very similar to that of the unsupported atomic layer.

1978 - Linear-Combination-of-Atomic-Orbital description of the electron states at the (0001) surfaces of hexagonal-close-packed metals [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; Manghi, Franca
abstract

The tight-binding method for calculating the electronic structure of a slab of regulary stacked atomic planes has been extended to treat the case of a (0001) surface of a hexagonal-close-packed (hcp) transition metal. The symmetry of the Hamiltonian is discussed and the basis functions of the representations along high-symmetry lines of the two-dimensional Brillouin zone are given. The theory is applied to the study of a 13-layer slab of hcp scandium. We find that several surface states and resonances arise in the d-band region and we discuss the effects of the self-consistency on these surface features. Possible experiments to test the theoretical results are suggested.

1978 - Surface bands in relaxed cleavage surface of GaP [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We have studied the dependence of the surface states upon relaxation in GaP (110) surface. Calculations were performed using a tight binding model with an approximate treatment of the self‐consistency. Different relaxation models, involving both rotation and stretching of the bonds were considered. The location and orbital composition of the surface bands their dispersion and the local density of states at the surface are presented for the various models. Unlike the other III–V compounds, we find that the relaxation does not remove the empty surface states from the band gap. Such a conclusion agrees with the experimental information on the pinning of the Fermi level in n‐doped samples of GaP. A comparison with partial‐yield photoemission data and a theoretical estimate of the surface excitonic binding energy are also given.

1978 - Surface bands of Ga containing III-V compounds [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present calculations of the electronic structure of the relaxed (110) face of all the Ga containing III-V materials. Surface features are identified either by their location inside gaps of the projected bulk band structure or by the localization of the wave function near the surface. The calculation provides the first accurate description of the surface electronic structure of Ga containing III-V compounds and explain the main trends of the experimental data.

1978 - Surface electronic states at the (110) surfaces of III-V compounds [Relazione in Atti di Convegno]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present a theroetical investigation of the effects of surface relaxation on the electronic structure of the cleavage faces of III-V compounds

1977 - A self-consistent calculation of the electronic structure of thin copper films [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We calculated the electronic structure of Cu films one, two and four layers thick using a tight-binding approach. An iterative procedure was used in order to dispose of the self-consistency requirements arising from the changes in the fractional occupancies of the various orbitals. The results show that the electronci structure for films of small thickness is intermediate between that of an isolated atom and that of a perfect crystal. A detailed comparison with previous theoretical work is presented, and the source of the various discrepancies is discussed.

1977 - Absence of filled surface states in the s-p gap of clean (111) surface of Ag [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; Manghi, Franca
abstract

The nature and location of the surface states, present at the (111) face of Ag, are investigated through a theoretical calculation of the band structure and local density of states based on a LCAO method. Previous assignments of surface structures in the photoemission spectra are critically discussed in the light of our results.

1977 - Dispersion of surface bands in W(100) surface [Articolo su rivista]
Bisi, Olmes; CALANDRA BUONAURA, Carlo; P., Flaviani; Manghi, Franca
abstract

The dispersion of the d surface bands and resonances along high symmetry directions of the two dimensional Brillouin zone has been calculated theoretically for the (001) face of W. The results show a variety of surface states, not specifically connected with the opening of spin orbit gaps.

1977 - ELECTRONIC-STRUCTURE AND ATOMIC CONFIGURATION AT CLEAVAGE SURFACE OF ZINCBLENDE COMPOUNDS [Articolo su rivista]
CALANDRA BUONAURA, Carlo; Manghi, Franca; Bertoni, Carlo Maria
abstract

The role of self-consistency and of the atomic distortions in determining the electronic structure of the cleavage surfaces of GaAs and ZnSe has been investigated using the layer method and an iterative tight-binding approach, which takes account of the difference between the surface and bulk electronic configurations. Several surface bands and resonances are identified near the gaps and empty lenses of the projected bulk band-structure and their sensitivity to the modifications of the surface potential are discussed. In the case of GaAs the inclusion of the atomic distortions at the surface is essential in order to obtain theoretical results in reasonable agreement with the experimental data. For ZnSe the available experimental information does not permit discrimination between the ideal and distorted configuration of the surface atoms, in spite of the sensitivity of the occupied surface states to the atomic displacements.

1977 - Electronic properties of clean (001) surfaces of Ir and Pt [Articolo su rivista]
Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present a theoretical investigation of the electronic structure of the ideal (001) surface of Ir and Pt. Surface band structures and local densities of states have been determined using a parametrized linear combinatiion of atomic orbitals for a film of fourteen (001) atomic planes. Various surfaces states and resonances arise in correspondence of the gaps of the projected bulk band structure. Our results explain the experimetnal data, obtained in field ion emission and conventional photoemission experiments, showing a surface sensitive structure in the proximity of the Fermi energy.

1977 - Surface bands of the (001) surface of molybdenum [Articolo su rivista]
Bertoni, Carlo Maria; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

The electronic structure of the ideal (001) surface of Mo is calculated using a parametrized linear combination of atomic orbitals. Surface states and resonances are identified along the high symmetry directions of the two dimensional Brillouin zone. The local density of states near the surface is presented and the main modifications due to the surface states are discussed. Significant surface features are found in the range 0–0.1 Ryd below the Fermi energy in agreement with the experimental findings.

1977 - The electonic structure of the (100) surface of Copper [Articolo su rivista]
Bertoni, Carlo Maria; Bisi, Olmes; CALANDRA BUONAURA, Carlo; Manghi, Franca
abstract

We present the results of a new calculation of the electronic structure of the (001) surface of Cu, obtained by using the layer method and a tight-binding description of the electron states. The selfconsistency requirements arising from the surface charge transfer are treated by assuming a charge and configuration dependence of the intraatomic matrix elements. It is found that, at variance with what obtained for other transition metals, the self-consistency plays a crucial role in determining the nature and the location of the surface states. A detailed discussion of the main surface features in the layer band structure and in the local densities of states at the topmost layers is given together with a comparison with previous theoretical work. The results are discussed in the light of the available experimental data.