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  • 1
    Electronic Resource
    Electronic Resource
    Interaction of methanol with Broensted acid sites of zeolite catalysts: an ab initio study (1995)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 3780-3789 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00118a014
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  • 2
    Electronic Resource
    Electronic Resource
    Proton NMR chemical shift and intrinsic acidity of hydroxyl groups. Ab initio calculations on catalytically active sites and gas-phase molecules (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 7833-7838 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00070a032
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular models in ab initio studies of solids and surfaces: from ionic crystals and semiconductors to catalysts (1989)
    s.l. : American Chemical Society
    Chemical reviews 89 (1989), S. 199-255 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr00091a006
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  • 4
    Electronic Resource
    Electronic Resource
    Gas phase acidities and molecular geometries of H3SiOH, H3COH, and H2O (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2575-2583 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical predictions are made by the coupled pair functional method employing large basis sets, [6s,5p,2d,1f/5s,3p,2d,1f/3s,2p] for geometries and [6s,5p,2d,1f/8s,5p,3d,1f/4s,2p] for deprotonation energies. The geometries obtained for H2O and CH3OH agree with the observed ones within the experimental uncertainty limits. The predicted equilibrium geometry (picometers, degrees) for silanol is r(SiO)=165.0, r(OH)=95.76, r(SiH)=146.8 (in plane), r(SiH)=147.6 (out of plane), angle (SiOH)=117.7. Nuclear motion corrections to geometries and vibrational contributions to deprotonation energies are considered. The predicted gas phase acidities (ΔH0298) are 392.3 (H2O), 384.5 (CH3OH), and 359.3 (SiH3OH) kcal/mol. The differences are discussed in terms of the potential on the acidic proton as well as of contributions from rearrangement of electrons and relaxation of nuclei. The remaining basis set error is assessed on calculations for H2O which employ a [10s,8p,4d,2f,1g/7s,3p,1d] basis set. The best theoretical estimate of ΔH0298 for H2O is 391.0±2.5 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458897
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  • 5
    Electronic Resource
    Electronic Resource
    The electronic states of Fe2S2−/0/+/2+ (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 617-628 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative energies of a multitude of low-lying electronic states of Fe2S2−/0/+/2+ have been determined by complete active space self-consistent-field (CASSCF) calculations. For selected states dynamical correlation has been included by the multireference configuration interaction method (MRCI) and the structures of some high-spin states have been optimized by CASSCF/MRCI. Comparison is made with structures obtained by density functional calculations. In all oxidation states of Fe2S2 the numerous states are assigned to spin ladders. The ground states of Fe2S2−/0/+/2+ are 10Ag, 1Ag, 2B1u and 1Ag, respectively. The total splittings of the lowest-energy spin ladders of Fe2S2, Fe2S2−, and Fe2S2+ are about 0.17, 0.18, and 0.35 eV, respectively. The spin ladders of Fe2S2 qualitatively reflect the picture of Heisenberg spin coupling. Some of the spin ladders of Fe2S2+ show the picture of combined Heisenberg coupling and double exchange. The calculated adiabatic electron affinity of Fe2S2 is 1.1 eV (observed 2.1 eV). Our estimate of the ionization energy of Fe2S2 is 7.9±0.5 eV. An interpretation of the observed photoelectron spectrum of Fe2S2− is given. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1424927
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  • 6
    Electronic Resource
    Electronic Resource
    Finding transition structures in extended systems: A strategy based on a combined quantum mechanics–empirical valence bond approach (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6983-6996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for efficient localization and description of stationary points on the potential energy surface of extended systems is presented. It is based on Warshel's empirical valence bond approach, for which we propose a modification, and combines the potential function description of the total system with a quantum mechanical description of the reaction site (QM-Pot). We describe the implementation of the method in the QMPOT program, which is basically an optimizer for minima and saddle points and has interfaces to existing quantum mechanical (e.g., TURBOMOLE, GAUSSIAN94) and interatomic potential function codes (e.g., GULP, DISCOVER). The power of the method is demonstrated for proton transfer reactions in zeolite catalysts, which may have as many as 289 atoms in the unit cell. As a test case the zeolite chabazite is considered in this study. Its limited unit cell size (37 atoms) makes comparison with the full periodic ab initio limit possible. The inclusion of long-range effects due to the periodic crystal structure by the QM-Pot method proves crucial in obtaining reliable results. The combined quantum mechanics–interatomic potential function calculations yield reaction barriers within 6 kJ/mol and reaction energies within 3.5 kJ/mol of the periodic ab initio limit. The zero-point vibrational energy corrected reaction barriers are between 58 and 97 kJ/mol for the six different proton jump paths. These are density functional results employing the B3LYP functional. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481296
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic structure and magnetic coupling in sodium electro sodalite: All-electron density functional calculations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5466-5476 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spin density functional calculations employing the full potential linearized augmented plane wave method (FLAPW) are performed on the periodic structure of sodium electro sodalite. The density functional adopted (PW91) includes gradient corrections for exchange and correlation. A body-centered cubic lattice of bare Na43+ clusters is found to be metallic and diamagnetic. The presence of the aluminosilicate framework makes it an antiferromagnetic material with a gap of about 0.1 eV between valence and conduction band. The antiferromagnetic state is more than 110–170 kJ mol−1 more stable than a ferromagnetic state. The Heisenberg exchange integrals between nearest and next nearest neighboring Na43+ clusters, Jnn and Jnnn, are derived from an extended Hückel tight-binding approach. The parameters of this Hamiltonian were chosen such that the density functional band structure is reproduced. The Heisenberg exchange integrals between nearest and next nearest neighboring Na43+ sites, Jnn and Jnnn, are negative, i.e., both nn and nnn sites are coupled antiferromagnetically. In absolute terms Jnnn is 0.6 meV. Estimates of Jnn are between 6.4 and 9.5 meV, the most likely value being 8.1±0.5 meV. Using these values for Jnn and Jnnn the molecular field approximation yields Weiss temperatures between −160 and −230 K. The most likely result, −200±10 K, fits well to the experimental value of about −200 K. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290006
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  • 8
    Electronic Resource
    Electronic Resource
    Vibrational spectra of the methanol tetramer in the OH stretch region. Two cyclic isomers and concerted proton tunneling (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2623-2628 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Second order Møller–Plesset perturbation theory and density functional theory are employed to localize several stationary points on the potential energy surface of the cyclic methanol tetramer. Two cyclic isomers are identified: one of S4 symmetry, with methyl groups in up-down-up-down configuration, and a second one of Ci symmetry, with the methyl groups in up-up-down-down configuration. The latter minimum is 360 cm−1 above the S4 minimum, with a barrier of 475 cm−1 separating them. These isomers give rise to four asymmetric OH modes around 3300 cm−1. A model of the concerted proton transfer, S4→D2d→S4 (D2d is the transition structure), yields an estimate of 0.7 cm−1 for the tunneling splitting of the totally symmetric OH stretch vibrational fundamental. Raman spectra would show evidence of this fundamental and help to identify admixtures of the Ci isomer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319647
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum chemical investigation of interaction sites in zeolites and silica (1980)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 84 (1980), S. 3318-3326 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100461a036
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular structure of orthosilicic acid, silanol, and H3SiOH.cntdot.AlH3 complex: models of surface hydroxyls in silica and zeolites (1987)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 91 (1987), S. 2315-2319 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100293a021
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