Foto personale

Francesco FAGLIONI

Department of Chemical and Geological Sciences

Fantini, Beatrice; Faglioni, Francesco ( 2016 ) - Computational Study of the Stability of Nanotube Fragments - CHEMISTRY-A EUROPEAN JOURNAL - n. volume 22 - pp. da 15501 a 15507 ISSN: 0947-6539 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Extremely short (<1 nm) fragments of zig-zag carbon nanotubes are studied with ab-initio techniques to determine their geometric and electronic structure as well as their magnetic susceptibility. It is found that for lengths of a few carbon–carbon bonds, each fragment can be viewed as composed of crowns, that is, zig-zag rings of carbon atoms along the circumference of the tube. In this case, two kinds of electronic structures are found, depending on whether the number of carbon atoms in each crown is even or odd. Systems comprising three or more crowns either have a high spin ground state or involve a charge transfer across the length of the fragment. Conjugation changes qualitatively when the length of the fragment approaches and surpasses its girth. Indications regarding the predicted chemical stability and electronic response are provided and interpreted in terms of current densities induced within each crown by a magnetic field along the tube axis.

Faglioni, Francesco; Merinov, Boris V.; Goddard, William A. ( 2016 ) - Room-Temperature Lithium Phases from Density Functional Theory - JOURNAL OF PHYSICAL CHEMISTRY. C - n. volume 120 - pp. da 27104 a 27108 ISSN: 1932-7447 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Metallic lithium is a promising electrode material for developing next generation rechargeable batteries, but it suffers from dendrite formation upon recharging. This compromises both efficiency and safety of these systems. The surface phenomena responsible for dendrite formation are difficult to characterize experimentally, making it important to use Quantum Mechanics (QM) to provide the understanding needed to design improved systems. The most accurate practical level of QM for such studies is the PBE form of density functional theory (DFT.) We report here an assessment of the accuracy for PBE to predict the most stable four phases of bulk lithium. PBE predicts three phases, bcc, fcc, and hcp, to be nearly equal in stability (within 5 meV). Including the zero-point energy and enthalpy corrections at standard conditions (298 K and 1 atm), we predict bcc most stable, fcc at 0.0029 eV, hcp at 0.0036 eV, and cI16 at 0.0277 eV. Indeed their experimental free energies under ambient conditions differ only by a few meV, with bcc considered most stable. Experimentally, the fourth phase becomes stable at high pressure (>30-40 GPa) and low temperature (<200 K). To use QM calculations to predict growth mechanisms, it is essential to bias the calculations by imposing the desired crystal structure in the underlying layers. We consider that this will allow QM studies of dendritic growth far from the crystalline phase due to the lower surface energy of bcc. (Figure Presented).

Stefano Pelloni; Francesco Faglioni; Paolo Lazzeretti ( 2013 ) - Chiral discrimination via nuclear magnetic resonance spectroscopy - RENDICONTI LINCEI. SCIENZE FISICHE E NATURALI - n. volume 24 - pp. da 283 a 289 ISSN: 2037-4631 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Calculations of nuclear magnetic shielding polarisabilities of cyclic C4H2X2 molecules, for X = O, S, Se and Te, have been carried out. Pseudoscalars of the nuclear magnetic shielding polarisability computed for the heavier nuclei are at least two orders of magnitude larger than those reported so far. Calculations of the rf voltage produced by the rotating chiral electric polarisation, induced by the permanent magnetic dipole moment of 77Se nucleus in 1,2-diselenin and 125Te nucleus in 1,2-ditellurin, are predicted to be &40 nV and &80 nV, respectively, detectable in principle with a proper experimental set-up. Also the chiral chemical shifts are evaluated and they are found near the experimental detection limit.

Stefano Pelloni; Francesco Faglioni; Paolo Lazzeretti ( 2013 ) - Parity violation energies of C_4 H_4 X_2 molecules for X=O, S, Se, Te and Po - MOLECULAR PHYSICS - n. volume 111 - pp. da 2387 a 2391 ISSN: 0026-8976 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Parity-violating contributions, with the same magnitude but opposite sign, to the energies of 1,2 enantiomers of dioxin, dithiin, diselenin, ditellurin, and dipolonin have been calculated. Theoretical predictions, which can be classified among the largest reported so far, indicate that the P enantiomer is energetically more stable than M. As expected, non-relativistic effects increase with the first power of the neutron number and the fourth power of the atomic number for X= O, S, Se, Te, Po. The trend predicted by Laerdahl and Schwerdtfeger [Phys. Rev. A {60}, 4439 (1999)] and by Berger [J. Chem. Phys. {129}, 154105 (2008)] for H_2X_2 molecules, characterized by free rotation about the X-X internuclear axis, is therefore confirmed for the series of more rigid C_4 H_4 X_2 compounds, in which limited deformations can take place.

V.S. Bryantsev; F. Faglioni ( 2012 ) - Predicting autoxidation stability of ether- and amide-based electrolyte solvents for Li-air batteries - JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY - n. volume 116 - pp. da 7128 a 7138 ISSN: 1089-5639 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Finding suitable solvents remains one of the most elusive challenges in rechargeable, nonaqueous Li-air battery technology. Although ether and amides are identified as stable classes of aprotic solvents against nucleophilic attack by superoxide, many of them are prone to autoxidation under oxygen atmosphere. In this work, we use density functional theory calculations coupled with an implicit solvent model to investigate the autoxidative stability of ether- and N,N-dialkylamide-based solvents. The change in the activation free energy for the C-H bond cleavage by O 2 is consistent with the extent of peroxide production for each class of solvent. Conversely, the thermodynamic stability alone is not sufficient to account for the observed variation in solvent reactivity toward O 2. A detailed understanding of the factors influencing the autoxidative stability provides several strategies for designing molecules with enhanced air/O 2 stability, comparable or superior to that of structurally related hydrocarbons. The mechanism of superoxide-mediated oxidation of hydroperoxides derived from ethers and amides is presented. The degradation mechanism accounts for the primary decomposition products (esters and carboxylates) observed in the Li-air battery with ether-based electrolytes. The identification of solvents having resistance to autoxidation is critical for the development of rechargeable Li-air batteries with long cycle life.

F. Faglioni; I Garcia Cuesta ( 2011 ) - Parity-Violation Energy of Biomolecules-IV: Protein Secondary Structure - ORIGINS OF LIFE AND EVOLUTION OF THE BIOSPHERE - n. volume 41 - pp. da 249 a 259 ISSN: 0169-6149 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The parity-violation energy difference between enantiomeric forms of the same amino acid sequence, from the amyloid beta-peptide involved in Alzheimer's desease, in both alpha-helix and beta-sheet configurations, is investigated with ab-initio techniques. To this end, we develop an extension of the N2 computational scheme that selectively includes neighboring amino acids to preserve the relevant H-bonds. In agreement with previous speculations, it is found that the helical alpha structure is associated with larger parity-violation energy differences than the corresponding beta form. Implications for the evolution of biological homochirality are discussed as well as the relative importance of various effects in determining the parity-violation energy.

Florini, Nicola; Faglioni, Francesco; Zucchi, Claudia; Caglioti, L.; Palyi, Gyula ( 2010 ) - Aqueous-phase quantitative NMR determination of amino acid enantiomer ratio by (13)C-NMR using chiral neodymium shift reagent - AMINO ACIDS - n. volume 38 - pp. da 1343 a 1350 ISSN: 1438-2199 [Articolo in rivista (262) - Articolo su rivista]
Abstract

A neodymium-(S)-PDTA (PDTA = N,N,N',N'-tetrakis[(hydroxycarbonyl)methyl]-1,2-diaminopropane) complex was found exceptionally useful in the quantitative determination of enantiomer ratios of water-soluble natural amino acids by (13)C-NMR. The method is demonstrated on mixtures of l- and d-enantiomers of various amino acids. The interactions of the chiral shift reagent with the amino acid molecules were rationalized by molecular orbital calculations.

Bryantsev, V. S.; Blanco, M.; Faglioni, Francesco ( 2010 ) - Stability of Lithium Superoxide LiO(2) in the Gas Phase: Computational Study of Dimerization and Disproportionation Reactions - JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY - n. volume 114 - pp. da 8165 a 8169 ISSN: 1089-5639 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Knowledge of the precise molecular mechanisms during the discharge and recharge processes in the lithium-air battery is critical for achieving desired improvements in specific capacity, current density, and cyclability. The initial oxygen reduction product formed in the presence of Li(+) ions is lithium superoxide LiO(2). In this study, we report the computed structures and thermodynamic parameters of LiO(2) dimerization in the gas phase, which enables us to provide a baseline for the reaction free energy profile of the subsequent disproportionation of (LiO(2))(2) to lithium peroxide Li(2)O(2) and O(2). Our calculations identified several low-lying (LiO(2))(2) dimers, with the singlet bipyramidal structure giving IR bands that are consistent with the characteristic IR vibration frequencies of (LiO(2))(2) in the oxygen matrix at T = 15-40 K. The activation barrier for (LiO(2))(2) = Li(2)O(2)+O(2) is 10.9 kcal/mol at the UCCSD(T)/CBS level (T = 298 K), suggesting that in the gas phase LiO(2) and its aggregates could only be observed at low temperatures.

L Caglioti; B Barabas; F Faglioni; N Florini; P Lazzeretti; M Maioli; K Micskei; K Rabai; F Taddei; C Zucchi; G Palyi; ( 2008 ) - On the track of absolute enantioselective catalysis - CHIMICA OGGI-CHEMISTRY TODAY - n. volume 26 - pp. da 30 a 32 ISSN: 0392-839X [Articolo in rivista (262) - Articolo su rivista]
Abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e. e.-s amplified by AES. These initial e. e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

Caglioti L; Barabas B; Faglioni F; Florini N.; Lazzeretti P.; Maioli M; Micskei K; Rabai G; Taddei F; Zucchi C; Palyi G ( 2008 ) - On the track of absolute enantioselective catalysisAuthor(s): Caglioti L, Barabas B, Faglioni F, et al.Source: CHIMICA OGGI-CHEMISTRY TODAY Volume: 26 Issue: 5 Pages: 30-32 Supplement: Suppl. 1 Published: SEP-OCT 2008 - CHIMICA OGGI - n. volume 26 - pp. da 30 a 32 ISSN: 1973-8250 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e. e.-s amplified by AES. These initial e. e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

B. Barabas; L. Caglioti; F. Faglioni; N. Florini; P. Lazzeretti; M.Maioli; K. Micskei; G. Rabai; F. Taddei; C. Zucchi; G. Palyi ( 2007 ) - On the traces of absolute enantioselective synthesis - COMPUTATION IN MODERN SCIENCE AND ENGINEERING VOL 2, PTS A AND B Book Series: AIP CONFERENCE PROCEEDINGS - n. volume 2 - pp. da 1150 a 1152 ISSN: 0094-243X [Abstract in Atti di convegno (274) - Abstract in Atti di Convegno]
Abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e.e.-s amplified by AES. These initial e.e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

F. FAGLIONI; P.LAZZERETTI; G.PALYI ( 2007 ) - Parity violation energy of 5-pyrimidyl alkanol, a chiral autocatalytic molecule - Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598 ) - CHEMICAL PHYSICS LETTERS - n. volume 435 - pp. da 346 a 349 ISSN: 0009-2614 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The energy of parity-violation due to weak-nuclear interactions between molecular electrons and nucleons associated with three molecules that participate in highly enantioselective autocatalytic reactions is estimated with ab initio techniques. The molecules, derivatives of (S)-5-pyrimidyl alkanol, are found to have very small parity-violation energy. Although our results are not conclusive, the computed parity-violation energy is not expected to have any effect on the direction of spontaneous symmetry breaking reported in the literature and leading to a preferential formation of the (S) form.

Q.MA; D.CHAKRABORTY; F. FAGLIONI; R.P.MULLER; W.A.GODDARD III ( 2006 ) - Alkylation of Phenol: A Mechanistic View - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY - n. volume 110 - pp. da 2246 a 2252 ISSN: 1089-5639 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products.

F. Faglioni; IG Cuesta; P. Lazzeretti ( 2006 ) - Parity violation energy of biomolecules - III: RNA - CHEMICAL PHYSICS LETTERS - n. volume 432 - pp. da 263 a 268 ISSN: 0009-2614 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The energy of parity-violation associated with a typical RNA double helix is estimated with ab initio techniques. It is shown that weak nuclear interactions do not favour the formation of the double helices found in nature. Possible implications regarding the potential effect on the evolution of biological homochirality are discussed.

STEFANO PELLONI; FRANCESCO FAGLIONI; RICCARDO ZANASI; P. LAZZERETTI ( 2006 ) - Topology of magnetic-field induced current-density field in diatropic mono-cyclic molecules - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW A - n. volume 74 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Concise information on the general features of the quantum-mechanical current density induced in the electrons of a molecule by a spatially uniform, time-independent magnetic field is obtained via a stagnation graph that shows the isolated singularities and the lines at which the current-density vector field vanishes. Stagnation graphs provide compact description of current-density vector fields and help the interpretation of molecular magnetic response, e.g., magnetic susceptibility and nuclear magnetic shielding. The stagnation graph of six cyclic, planar aromatic molecules has been obtained at the Hartree-Fock level via a procedure based on continuous transformation of the origin of the current density formally annihilating the diamagnetic contribution. Some common distinctive elements observed for cyclic aromatic rings CnHn, with n=3,4, . . . ,8, in the presence of a magnetic field normal to the molecular plane, are discussed. The results can be used for a general discussion of diatropism in aromatic systems.

S.PELLONI; F. FAGLIONI; R.ZANASI; P.LAZZERETTI ( 2006 ) - Topology of magnetic-field-induced current-density field in diatropic monocyclic molecules - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW A - n. volume 74 - pp. da 012506 ISSN: 1050-2947 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Concise information on the general features of the quantum-mechanical current density induced in the electrons of a molecule by a spatially uniform, time-independent magnetic field is obtained via a stagnation graph that shows the isolated singularities and the lines at which the current-density vector field vanishes. Stagnation graphs provide compact description of current-density vector fields and help the interpretation of molecular magnetic response, e.g., magnetic susceptibility and nuclear magnetic shielding. The stagnation graph of six cyclic, planar aromatic molecules has been obtained at the Hartree-Fock level via a procedure based on continuous transformation of the origin of the current density formally annihilating the diamagnetic contribution. Some common distinctive elements observed for cyclic aromatic rings CnHn, with n=3,4,...,8, in the presence of a magnetic field normal to the molecular plane, are discussed. The results can be used for a general discussion of diatropism in aromatic systems.

F. FAGLIONI; W.A.GODDARD III ( 2005 ) - Energetics of hydrogen coverage on group VIII transition metal surfaces and a kinetic model for adsorption/desorption - THE JOURNAL OF CHEMICAL PHYSICS - n. volume 122 - pp. da 014704 ISSN: 0021-9606 [Articolo in rivista (262) - Articolo su rivista]
Abstract

We determined the binding energy of hydrogen to the closest packed surface for all nine group VIII transition metals as a function of surface coverage using quantum mechanics (density functional theory with the generalized gradient approximation) with periodic boundary conditions. The study provides a systematic comparison of the most stable surfaces of the nine group VIII transition metals, leading to results consistent with available surface science studies. We then use these to develop a simple thermodynamic model useful in estimating the surface coverage under typical heterogeneous catalysis conditions and compare these results to temperature programmed desorption experiments.

Francesco Faglioni;Alessio Passalacqua;Paolo Lazzeretti ( 2005 ) - Parity Violation Energy Of Biomolecules – I: Polypeptides - ORIGINS OF LIFE AND EVOLUTION OF THE BIOSPHERE - n. volume 35 - pp. da 461 a 475 ISSN: 0169-6149 [Articolo in rivista (262) - Articolo su rivista]
Abstract

A computational algorithm is developed to compute the energy of parity-violation (E-pv) due to weak-nuclear forces acting within chain polymers. The method is applied to estimate the magnitude of E-pv associated with the folding of alpha-helices in polypeptide chains and, in turn, of typical proteins. Implications to the development of biological homochirality in nature are discussed in terms of a simple evolutionary model to assess the likelihood for energies of the order of the computed E-pv to have determined the direction of natural homochirality.

F. Faglioni; P.S. D'Agostino; B. Cadioli; P. Lazzeretti ( 2005 ) - Parity violation energy of biomolecules - II: DNA - CHEMICAL PHYSICS LETTERS - n. volume 407 - pp. da 522 a 526 ISSN: 0009-2614 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The energy of parity-violation associated with a typical DNA double helix is estimated with ab initio techniques. It is shown that weak-nuclear interactions do not favor the formation of the double helices found in nature. Possible implications regarding the potential effect of parity-violation interactions on the evolution of biological homochirality are discussed.

MB Ferraro; F. Faglioni; A. Ligabue; S. Pelloni; P. Lazzeretti ( 2005 ) - Ring current effects on nuclear magnetic shielding of carbon in the benzene molecule - MAGNETIC RESONANCE IN CHEMISTRY - n. volume 43 - pp. da 316 a 320 ISSN: 0749-1581 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The differential Biot-Savart law of classical electrodynamics was applied to develop a ring current model for the magnetic shielding of the carbon nucleus in benzene. It is shown that the local effect of the pi currents, induced by a magnetic field normal to the molecular plane, on the sigma(C) out-of-plane shielding tensor component vanishes. However, approximately 10% of sigma(C) is due to the shielding contributions from pi current density in the region of the other carbon atoms. Magnetic shielding density maps obtained via quantum mechanical procedures confirm the predictions of the classical model.

F. FAGLIONI; A. LIGABUE; S. PELLONI; A. SONCINI; P. LAZZERETTI ( 2004 ) - Molecular response to a time-independent non-uniform magnetic-field - CHEMICAL PHYSICS - n. volume 304 - pp. da 289 a 299 ISSN: 0301-0104 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The response of a molecule to a static inhomogeneous magnetic-field is rationalized via multipole magnetic susceptibilities and induced magnetic multipole and anapole moments. The energy of the molecule interacting with the external field is expressed as a Taylor series in the powers of the field and its gradient at the origin of the coordinate system. It involves magnetic multipole tensors of increasing rank, which can be evaluated via quantum mechanical approaches. An electronic energy shift is caused by the feedback interaction between the induced magnetic dipole moment and the external magnetic field, and between the induced magnetic quadrupole moment and the gradient of the magnetic field. It is shown that, for a static magnetic field with uniform gradient, the magnetic quadrupole moment is origin-dependent, but the total interaction energy and the induced magnetic dipole are invariant to a translation of the coordinate system. The formal advantages of a Geertsen approach to third- and fourth-rank mixed-multipole susceptibilities are discussed.

P.SCHWERDTFEGER; A.KUEHN; R.BAST; J.K.LAERDAHL; F. FAGLIONI; P.LAZZERETTI ( 2004 ) - The vibrational spectrum of camphor from ab initio and density functional theory and parity violation in the C-C*-CO bending mode - Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598 ) - CHEMICAL PHYSICS LETTERS - n. volume 383 - pp. da 496 a 501 ISSN: 0009-2614 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The C-C*-CO bending mode in camphor (C* denotes a chiral carbon) as originally investigated for parity violation effects by Arimondo et al. [Opt. Commun. 23 (1977) 369] lies in the CO2 laser frequency range with the most intense transition at 1045 cm(-1). The vibrational spectrum of camphor is, therefore, reinvestigated by ab initio and density functional calculations and compared with experimental results. This provides the basis for a local mode analysis which reveals that the C-C*-CO bending mode has only minute parity violation contributions (<10(-5) Hz) to vibrational transitions far below the current detection limit of high resolution spectroscopy.

S. Pelloni; F. Faglioni; A. Soncini; A. Ligabue; Lazzeretti P. ( 2003 ) - Magnetic response of dithiin molecules: is there anti-aromaticity in nature? - CHEMICAL PHYSICS LETTERS - n. volume 375 - pp. da 583 a 590 ISSN: 0009-2614 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Ab initio current density formalism is used to investigate the response to external magnetic fields of the only knownnaturally occurring moieties which are formally anti-aromatic, i.e., dithiines. Magnetic susceptibility, nuclear shieldingconstants, and the topology of induced current densities indicate that although these molecules satisfy H€uckels rule forbeing anti-aromatic, they are not. In chiral dithiines, the multipolar expansion of the response contains non-vanishinganapole terms associated with spinning cuff current lines.

A. SONCINI; F. FAGLIONI; P. LAZZERETTI ( 2003 ) - Parity Violating Contributions to Nuclear Magnetic Shielding. - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW A - n. volume 68 [Articolo in rivista (262) - Articolo su rivista]
Abstract

A gauge-invariant formalism is developed to describe the effect of parity-violating weak-nuclear interactionson nuclear magnetic chemical shift in molecules. Such effect is computed for two molecules with ab initiotechniques and it is found to be orders of magnitude smaller than experimental resolution for the moleculesconsidered.

F. FAGLIONI; P. LAZZERETTI ( 2003 ) - Parity-Violation Effect on Vibrational Spectra - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW A - n. volume 67 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Weak nuclear coupling between the nucleons of a molecule and its electrons causes the energy and electronic wave function to be different for two enantiomers of a chiral molecule, i.e., for two molecules which are the specular image of each other. Although this effect has been known for some time, its magnitude is so small that all attempts made so far at measuring it experimentally have failed. We report in this paper computational estimates of vibrational frequency shifts due to parity-violation energy near or above current experimental resolution. Our findings indicate that an experimental evidence of parity-violation effects in molecular systems is within reach.

F. FAGLIONI; M.BLANCO; W.A.GODDARD III; D.SAUNDERS ( 2002 ) - Heterogeneous Inhibition of Homogeneous Reactions: Karstedt Catalyzed Hydrosilylation - American Chemical Society, Washington, D.C. ) - JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL - n. volume 106 - pp. da 1714 a 1721 ISSN: 1520-6106 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The Karstedt-catalyzed hydrosilylation reaction used in curing of silicone release coatings was investigated using first-principle quantum mechanical techniques (density functional theory) as well as semiempirical methods to estimate solubility parameters. The results we obtain for the catalytic cycle indicate, in agreement with experimental results, that hydrosilylation occurs easily at room temperature. The detailed mechanism we suggest contains the key features of the models previously proposed in the literature by Lewis and Chalk-Harrod and adds quantitative estimates of reaction energies and barriers. On the basis of the energy profile for the catalytic cycle in the presence of inhibitor molecules and on solubility parameters for the species involved in the reaction, we conclude that the role of the inhibitors we considered is to phase-separate the catalyst from the substrate. The reaction is thus quenched by introducing a microscopic second phase that interferes with the homogeneous reaction.

X.XU; F. FAGLIONI; W.A.GODDARD III ( 2002 ) - Methane Activation by Transition-Metal Oxides, MOx (M=Cr, Mo, W; x=1,2,3) - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - JOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY - n. volume 106 - pp. da 7171 a 7176 ISSN: 1089-5639 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Recent experiments on the dehydrogenation-aromatization of methane (DHAM) to form benzene using a MoO3/HZSM-5 catalyst stimulated us to examine methane activation by the transition-metal oxide molecules, MOx (M = Cr, Mo, W; x = 1, 2, 3). The present studies use hybrid density functional theory (B3LYP). The reactivity trend is rationalized in terms of changes in the electrophilicity of MO,, the strength of the M-O pi bond, and the bonding properties of MQ(x) to methyl or hydrogen as M and x are varied, It is found that or-bond metathesis to the metal hydride product (H-MOx-1-OCH3) occurs preferentially over the high oxidation state form (MO3) of the heavier metals, as well as all chromium oxides (CrOx). Instead, oxidative addition of MOx leading to methyl metal hydride (H-M(O-x)-CH3) is more favorable over the low oxidation state of MOx (M = Mo, W, x = 2, 1). In particular, it is found that WO2 can undergo oxidative addition with negligible activation barrier and is predicted to be the most reactive compound of this class toward methane activation. Our finding that MO2 (M = W, Mo) is the best oxidation state for this class of metal oxides toward methane activation suggests that the MO3/HZSM-5 catalysts active in the DHAM reaction may be W and Mo oxycarbides (MO2C2). The formation of such intermediates may be the reason that the experiments find an induction period before the catalyst is active for the desired reaction.

F. Faglioni; Lazzeretti P. ( 2002 ) - Understanding Parity violation in molecular systems. - PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS - n. volume 65 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Parity-violation energy (EPV) due to weak nuclear interactions between nucleons and electrons in chiralmolecular systems provides a fundamental tool to verify our understanding of electronic behavior in complexsystems. We used both a relativistic and a nonrelativistic approach to study a number of simple molecules andanalyze the corresponding EPV in terms of intuitive electrodynamic concepts. We developed a qualitativemodel to predict the sign of EPV and its behavior against selected geometric distortions. Our model provides avaluable tool to screen large sets of molecules and select interesting candidates for more expensive investigations.

F. FAGLIONI; P.LAZZERETTI ( 2002 ) - Understanding parity violation in molecular systems - pubblicata da: AMERICAN PHYSICAL SOC, ONE PHYSICS ELLIPSE, COLLEGE PK, USA, MD, 20740-3844 ) - PHYSICAL REVIEW E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS - n. volume 65 - pp. da 011904 ISSN: 1539-3755 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Parity-violation energy (E(PV)) due to weak nuclear interactions between nucleons and electrons in chiral molecular systems provides a fundamental tool to verify our understanding of electronic behavior in complex systems. We used both a relativistic and a nonrelativistic approach to study a number of simple molecules and analyze the corresponding E(PV) in terms of intuitive electrodynamic concepts, We developed a qualitative model to predict the sign of E(PV) and its behavior against selected geometric distortions, Our model provides a valuable tool to screen large sets of molecules and select interesting candidates for more expensive investigations.

PP.KNOPS-GERRITS; P.A.JACOBS; A.FUKUOKA; M.ICHIKAWA; F. FAGLIONI; W.A.GODDARD III ( 2001 ) - Reactivity of methane mono-oxygenase, insights from quantum mechanic studies on synthetic iron model complexex - Elsevier BV:PO Box 211, 1000 AE Amsterdam Netherlands:011 31 20 4853757, 011 31 20 4853642, 011 31 20 4853641, EMAIL: nlinfo-f@elsevier.nl, INTERNET: http://www.elsevier.nl, Fax: 011 31 20 4853598 ) - JOURNAL OF MOLECULAR CATALYSIS. A: CHEMICAL - n. volume 166 - pp. da 3 a 13 ISSN: 1381-1169 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Methane mono-oxygenase (MMO) and deoxyhemerythrin (DHr) are examples of di-iron enzymes that catalyze the dissociative and non-dissociative binding of molecular oxygen. To mimic the MMO active site with a finite cluster, we chose to study the binuclear heptapodate coordinated iron(III)-complexes of N,N,N,N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diamino-propane (HPTB) and N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diamino-propane (HPTP). These have active sites of the form [Fez (HPTP)(mu -OH)](4+) (1) and [Fe-2(HPTB)(mu -OH)](4+) (2). Quantum mechanics structures are compared with the experimental data obtained from the EXAFS analysis. For the O-2 binding on the reduced active site. the mu-eta (1):eta (1)-O-2 mode seems the slightly more stable precursor to the O=Fe-O-Fe=O bis-ferryl (re)active site. The nature of the ferryl groups are these of a reactive two center three electron bond. (C) 2001 Elsevier Science B.V. All rights reserved.

N.S.LEWIS; C.L.CLAYPOOL; W.A.GODDARD III; F. FAGLIONI; H.B.GRAY; R.A.MARCUS ( 2001 ) - Scanning Tunneling Microscopy of Functional Groups: Substituted Alkanes and Alkanols on Graphite - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 221 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Scanning Tunneling Microscopy of Functional Groups: Substituted Alkanes and Alkanols on Graphite

GODDARD WA; MULLER R; KUA J; F. FAGLIONI; PHILIPP D; ET AL ( 2000 ) - Investigations of heterogeneous and homogeneous transition metal catalysis using density functional theory. - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 220 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Investigations of heterogeneous and homogeneous transition metal catalysis using density functional theory.

J.KUA; F. FAGLIONI; W.A.GODDARD ( 2000 ) - Thermochemistry for hydrocarbon intermediates chemisorbed on metal surfaces: CH{n-m}(CH3)m with n=1, 2, 3 and m >= n on Pt, Ir, Os, Pd, Ph, and Ru - [Washington, USA: American Chemical Society] 1879- ) - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - n. volume 122 - pp. da 2309 a 2321 ISSN: 0002-7863 [Articolo in rivista (262) - Articolo su rivista]
Abstract

To provide insight and understanding of the thermochemistry underlying hydrocarbon rearrangements on transition metal surfaces, we report systematic studies of hydrocarbon radicals chemisorbed on metal clusters representing the closest packed surfaces of the six second and third row group VIII transition metals. Using first principles quantum mechanics [nonlocal density functional theory with exact HF exchange (B3LYP)], we find that (i) CH3-m(CH3)(m) forms one bond to the surface, preferring the on-top site (eta(1)), (ii) CH2-m(CH3)(m) forms two bonds to the surface, preferring the bridge site (eta(2)), and (iii) CH1-m(CH3)(m) forms three bonds to the surface, preferring the 3-fold site (eta(3)). For all six metals, the adiabatic bond energy is nearly proportional to the number of bonds to the surface, but there are dramatic decreases in the bond energy with successive methyl substitution. Thus from CH3 to CH2CH3, CH(CH3)(2), and C(CH3)(3), the binding energy decreases by 6, 14, and 23 kcal/mol, respectively (out of similar to 50). From CH2 to CHCH3 and C(CH3)(2), the binding energy decreases by 8 and 22 kcal/mol, respectively (out of similar to 100). These decreases due to methyl substitution can be understood in terms of steric repulsion with the electrons of the metal surface. For CH to C(CH3), the bond energy decreases by 13 kcal/mol (out of similar to 160), which is due to electronic promotion energies. These results are cast in terms of a thermochemical group additivity framework for hydrocarbons on metal surfaces similar to the Benson scheme so useful for gas-phase hydrocarbons. This is used to predict the chemisorption energies of more complex adsorbates.

GODDARD WA; MULLER R; STRACHAN A; KUA J; F. FAGLIONI; ET AL ( 2000 ) - Tutorial: Case studies in the use of density functional theory for transition metal systems, with an emphasis on heterogeneous and homogeneous catalysis, metal alloys, and transition metal oxides. - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 220 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Tutorial: Case studies in the use of density functional theory for transition metal systems, with an emphasis on heterogeneous and homogeneous catalysis, metal alloys, and transition metal oxides.

F. FAGLIONI; P. LAZZERETTI ( 2000 ) - Understanding Parity violation in molecular systems - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW E - n. volume 65 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Parity-violation energy (EPV) due to weak nuclear interactions between nucleons and electrons in chiralmolecular systems provides a fundamental tool to verify our understanding of electronic behavior in complexsystems. We used both a relativistic and a nonrelativistic approach to study a number of simple molecules andanalyze the corresponding EPV in terms of intuitive electrodynamic concepts. We developed a qualitativemodel to predict the sign of EPV and its behavior against selected geometric distortions. Our model provides avaluable tool to screen large sets of molecules and select interesting candidates for more expensive investigations.

C.L.CLAYPOOL; F. FAGLIONI; A.J.MATZGER; W.A.GODDARD; N.S.LEWIS ( 1999 ) - Effects of molecular geometry on the STM image contrast of methyl- and bromo-substituted alkanes and alkanols on graphite - American Chemical Society, Washington, D.C. ) - JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL - n. volume 103 - pp. da 9690 a 9699 ISSN: 1520-6106 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Scanning tunneling microscopy (STM) images have been collected for a series of substituted alkanes and alkanols that form ordered overlayers at room temperature on highly ordered pyrolytic graphite surfaces. Molecules that have been imaged possess an internal bromide, with or without terminal alcohol groups (HO(CH2)(9)CHBr(CH2)(10)OH and H3C(CH2)(16)CHBr(CH2)(16)CH3), an internal -OH group (H3C(CH2)(16)CHOH(CH2)(16)CH3), and an internal methyl group (H3C(CH2)(16)CHCH3(CH2)(16)CH3). These data allow comparison to the STM image contrast reported previously for molecules in which -OH, -Br, and -CH3 groups were located in terminal positions of alkane chains adsorbed onto graphite surfaces. When the functional groups were in gauche positions relative to the alkyl chain, and thus produced molecular features that protruded toward the tip, the functional groups were observed to produce bright regions in a constant current STM image, regardless of the STM contrast behavior observed for these same functional groups when they were in terminal positions of adsorbed alkyl chains. These observations are in excellent agreement with theoretical predictions of the STM behavior of such systems. Additionally, several interesting packing structures have been observed that have yielded insight into the intermolecular forces that control the packing displayed by these overlayers.

P. LAZZERETTI; R. ZANASI; F. FAGLIONI ( 1999 ) - Energetic Stabilization of d-Camphor via Weak Neutral Currents - American Institute of Physics:2 Huntington Quadrangle, Suite 1NO1:Melville, NY 11747:(800)344-6902, (631)576-2287, EMAIL: subs@aip.org, INTERNET: http://www.aip.org, Fax: (516)349-9704 ) - PHYSICAL REVIEW E - n. volume 60 - pp. da 871 a 874 ISSN: 1063-651X [Articolo in rivista (262) - Articolo su rivista]
Abstract

It is shown via a series of numerical tests on the camphor molecule, C10H16O, that the naturally occurringd-enantiomer is energetically stabilized with respect to its mirror image by electroweak force. The calculatedenergy difference between enantiomers, about 1.5310219 hartree, is roughly eight orders of magnitude smallerthan the upper bound suggested by available spectroscopic investigations on the frequency of a spectroscopictransition. However, such a difference is about ten times larger than previous estimates of parity-violatingenergy contributions reported in the literature for other chiral molecules, which makes the idea of electroweakstabilization of one enantiomer more reliable than expected before.

F. FAGLIONI; W.A.GODDARD ( 1999 ) - GVB-RP: A reliable MCSCF wave function for large systems - -New York: Wiley. -Belgium: Uitj Kluwer Rechtswetenschappe ) - INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY - n. volume 73 - pp. da 1 a 22 ISSN: 0020-7608 [Articolo in rivista (262) - Articolo su rivista]
Abstract

We have developed a version of generalized valence bond (GVB) that overcomes the major weakness of the perfect pairing approximation without requiring a full transformation of the integrals at each step of the self-consistent orbital optimization. The method, called generalized valence bond-restricted pairing (GVB-RP), describes properly the dissociation of up to triple bonds and provides smooth potential energy surfaces for most chemical reactions. The wave functions obtained are a good starting point for more sophisticated computational techniques. The applicability of the method is illustrated with a few simple examples including multiple-bond dissociations, transition states for symmetry allowed, symmetry forbidden, and radical reactions, as well as reactions at a transition-metal center. The cost of the method compares well with other self-consistent correlated techniques.

W.A.GODDARD III; F. FAGLIONI; J.KUA; D.PHILLIP; M.FELDMANN; ET AL ( 1999 ) - MSC/Caltech Collaborations with Industry an Catalysis Technologies - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 219 [Articolo in rivista (262) - Articolo su rivista]
Abstract

MSC/Caltech Collaborations with Industry an Catalysis Technologies

C.L.CLAYPOOL; F. FAGLIONI; W.A.GODDARD; N.S.LEWIS ( 1999 ) - Tunneling mechanism implications from an STM study of H3C(CH2)15HC=C=CH(CH2)15CH3 on graphite and C14H29OH on MoS2 - American Chemical Society, Washington, D.C. ) - JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL - n. volume 103 - pp. da 7077 a 7080 ISSN: 1520-6106 [Articolo in rivista (262) - Articolo su rivista]
Abstract

The observations reported herein confirm that the bright spots in high-resolution STM images of adsorbed alkanes and alkanols are predominantly due to the electronic and topographic structure of the molecule, and not predominantly due to the substrate. STM images of a monolayer of 17,18-pentatriacontadiene, H3C(CH2)(15)-HC=C=CH(CH2)(15)CH3, adsorbed on graphite were obtained to evaluate whether changes in the orientation of the exposed methylene hydrogen atoms relative to the STM tip produced changes in the observed pattern of bright spots in a STM image. STM images of this system showed a pattern of bright spots within individual molecules that appears to change on either side of the allene -C=C=C- functionality. STM images were also obtained for tetradecanol overlayers on graphite and MoS2 surfaces. The angles and distances observed in the images of tetradecanol on MoS2 were nearly identical to those measured previously in our laboratories for alkanol and alkane monolayers on graphite despite that fact that the separation between bright spots in an STM image of graphite is 2.46 Angstrom, while the separation between bright spots in STM images of MoS2 is 3.16 Angstrom.

W.A.GODDARD; C.BRANDOW; C.KANKEL; J.SEFCIK; F. FAGLIONI ( 1998 ) - Transition states for homogeneous and heterogeneous catalysis, including stereoselective polymerizations and for metathesis. - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 2156 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Transition states for homogeneous and heterogeneous catalysis, including stereoselective polymerizations and for metathesis.

C.L.CLAYPOOL; N.S.LEWIS; F. FAGLIONI; W.A.GODDARD; H.B.GRAY; R.A.MARCUS ( 1998 ) - Why molecules look the way they do in STM: A systematic functional group approach. - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 216 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Why molecules look the way they do in STM: A systematic functional group approach.

C.L.CLAYPOOL; F. FAGLIONI; W.A.GODDARD; H.B.GRAY; N.S.LEWIS; R.A.MARCUS ( 1997 ) - Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite: A Systematic Functional Group Approach - American Chemical Society, Washington, D.C. ) - JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL - n. volume 101 - pp. da 5978 a 5995 ISSN: 1520-6106 [Articolo in rivista (262) - Articolo su rivista]
Abstract

A series of functionalized alkanes and/or alkyl alcohols have been prepared and imaged by scanning tunneling microscopy (STM) methods on graphite surfaces. The stability of these ordered overlayers has facilitated reproducible collection of STM images at room temperature with submolecular resolution, in most cases allowing identification of individual hydrogen atoms in the alkane chains, but in all cases allowing identification of molecular length features and other aspects of the image that can be unequivocally related to the presence of functional groups in the various molecules of concern. Functional groups imaged in this study include halides (X = F, Cl, Br, I), amines, alcohols, nitriles, alkenes, alkynes, ethers, thioethers, and disulfides. Except for -Cl and -OH, all of the other functional groups could be distinguished from each other and from -Cl or -OH through an analysis of their STM metrics and image contrast behavior. The dominance of molecular topography in producing the STM images of alkanes and alkanols was established experimentally and also was consistent with quantum chemistry calculations. Unlike the contrast of the methylene regions of the alkyl chains, the STM contrast produced by the various functional groups was not dominated by topographic effects, indicating that variations in local electronic coupling were important in producing the observed STM images of these regions of the molecules. For molecules in which electronic effects overwhelmed topographic effects in determining the image contrast, a simple model is presented to explain the variation in the electronic coupling component that produces the contrast between the various functional groups observed in the STM images. Additionally, the bias dependence of these STM images has been investigated and the contrast vs bias behavior is related to factors involving electron transfer and hole transfer that have been identified as potentially being important in dominating the electronic coupling in molecular electron transfer processes.

F. FAGLIONI; C.L.CLAYPOOL; N.S.LEWIS; W.A.GODDARD ( 1997 ) - Theoretical Description of the STM Images of Alkanes and Substituted Alkanes Adsorbed on Graphite - American Chemical Society, Washington, D.C. ) - JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL - n. volume 101 - pp. da 5996 a 6020 ISSN: 1520-6106 [Articolo in rivista (262) - Articolo su rivista]
Abstract

A theoretical model based on perturbation theory has been developed to predict the scanning tunneling microscopy (STM) images of molecules adsorbed on graphite, The model is applicable to a variety of different molecules with reasonable computational effort and provides images that are in qualitative agreement with experimental results. The model predicts that topographic effects will dominate the STM images of alkanes on graphite surfaces. The computations correlate well with the STM data of functionalized alkanes and allow assessment of the structure and orientation of most of the functionalized alkanes that have been studied experimentally. In addition, the computations suggest that the highly diffuse virtual orbitals of the adsorbed molecules, despite being much farther in energy from the Fermi level of the graphite than the occupied orbitals, may play an important role in determining the STM image contrast of such systems.

W.A.GODDARD; C.BRANDOW; F. FAGLIONI; E.P.BIERWAGEN ET AL ( 1996 ) - Theoretical-studies of Metallocene Polymerization Catalysts - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 211/2 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Theoretical-studies of Metallocene Polymerization Catalysts

W.A.GODDARD; K.T.LIM; M.BELMARES; Y.GUO; X.CHEN; F. FAGLIONI ( 1994 ) - Simulation and Design of Materials - Applications to Polymers, Ceramics, Semiconductors, and Catalysis - American Chemical Society:1155 Sixteenth Street Northwest:Washington, DC 20036:(800)227-5558, EMAIL: service@acs.org, INTERNET: http://www.pubs.acs.org, Fax: (614)447-3671 ) - ABSTRACTS OF PAPERS - AMERICAN CHEMICAL SOCIETY - n. volume 208/2 [Articolo in rivista (262) - Articolo su rivista]
Abstract

SIMULATION AND DESIGN OF MATERIALS - APPLICATIONS TO POLYMERS, CERAMICS, SEMICONDUCTORS, AND CATALYSIS

FAGLIONI F; LAZZERETTI P; MALAGOLI M; ZANASI R; PROSPERI T ( 1993 ) - CALCULATION OF INFRARED AND VIBRATIONAL CIRCULAR-DICHROISM INTENSITIES VIA NUCLEAR ELECTROMAGNETIC SHIELDINGS - THE JOURNAL OF PHYSICAL CHEMISTRY - n. volume 97 - pp. da 2535 a 2542 ISSN: 0022-3654 [Articolo in rivista (262) - Articolo su rivista]
Abstract

Infrared and vibrational circular dichroism intensities have been evaluated theoretically for trans-(1S,2S)-dideuteriooxirane, trans-(1S,2S)-dideuteriocyclopropane, (S)-propylene oxide, and trans-(1R,2R)-dimethyl-cyclopropane molecules, via electric and electromagnetic nuclear shielding tensors determined by random-phase approximation within the framework of 6-31g, 6-31g**, 6-31gext, and 6-31gpol Gaussian basis sets. Differentiation of matrix elements is avoided by the procedure adopted in this work. By comparing the results provided by several numerical tests it is found that reliable force fields of Hartree-Fock quality can be obtained at the 6-31g** and 6-31gex level; 6-31gpol basis provides the most accurate polar and axial atomic tensors. The nuclear shieldings are to be calculated with great accuracy in order to achieve a good prediction of the intensity patterns, as they bias the overall quality of theoretical oscillator strengths and rotational strengths. Comparison with available experimental data and previous ab initio calculations demonstrates the practicality of the present method for small and medium size molecules. The Hartree-Fock accuracy of the theoretical estimates of vibrational intensities is also proven by analyzing constraints for translational and rotational invariance which should be exactly fulfilled in the limit of complete basis sets. These results document the competitivity of the nuclear shielding method with the analytic derivative procedure.