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  • 1
    Electronic Resource
    Electronic Resource
    A quantum-mechanical study of the relative stability under pressure of MgSiO3-ilmenite, MgSiO3-perovskite, and MgO-periclase+SiO2-stishovite assemblage (1994)
    Springer
    Physics and chemistry of minerals 21 (1994), S. 285-293 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The relative stability of MgSiO3-ilmenite, MgSiO3-perovskite and (periclase+stishovite) assemblage phases as a function of the pressure is investigated with the periodic quantum mechanical ab initio HartreeFock program CRYSTAL. For the first time, the structure of MgSiO3-ilmenite is fully optimized. Basis set effects are explored. It turns out that relatively small basis sets reproduce correctly experimental geometries. However, larger basis sets (“triple zeta” quality, plus polarization d functions) are needed to yield significant thermochemical results. All contributions to the 0 K enthalpy are discussed. On the basis of the present highest level calculations, it appears that in the explored range of pressure (0〈P〈 60 GPa) the mineralogical assemblage periclase+stishovite has higher enthalpy than MgSiO3-ilmenite or perovskite, and that ilmenite transforms to orthorhombic perovskite around to 29.4 GPa in good agreement with experimental data extrapolated down to 0 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202092
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  • 2
    Electronic Resource
    Electronic Resource
    An ab initio Hartree-Fock study of silver chloride
    Amsterdam : Elsevier
    Chemical Physics Letters 186 (1991), S. 329-335 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(91)90187-E
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum-mechanical Hartree-Fock study of calcite (CaCO3) at variable pressure, and comparison with magnesite (MgCO3) (1993)
    Springer
    Physics and chemistry of minerals 20 (1993), S. 104-110 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The static crystal energy of calcite and its structure configuration as functions of pressure were determined by ab initio all-electron periodic Hartree-Fock calculations (CRYSTAL code). Ca, O and C atoms were represented by 22, 18 and 14 atomic orbitals, respectively, in form of contracted Gaussian-type functions. Comparison between theoretical and experimental data was performed for binding energy, equilibrium unit-cell and bond lengths, bulk modulus and C 33 and C 11 + C 12 elastic constants, and vibrational frequency of the symmetrical C-O stretching mode. The agreement is generally satisfactory. A larger compressibility is observed for structural parameters of calcite than for those of magnesite coming from a similar calculation. The Ca-O and C-O chemical bonding was characterized by electron density maps and by Mulliken atomic charges; these are discussed and compared to values determined by empirical fitting of Born-type interatomic potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207203
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  • 4
    Electronic Resource
    Electronic Resource
    Parallel computational chemistry made easier: The development of NWChem (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 475-483 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the design philosophy, structure, and supporting tool kits of the NWChem computational chemistry package. The primary purpose of this effort was to develop efficient parallel algorithms for a broad range of methods commonly used in computational chemistry. To facilitate this, we developed a shared nonuniform access memory model which simplifies parallel programming while at the same time providing for portability across both distributed- and shared-memory machines. In addition to this specific focus on parallelization, a substantial effort has been made to simplify the general problem of large-scale software development, which is common to many research groups. We find that this simplification can be achieved through judicious use of ideas from the computer science field of software engineering in the design and implementation of the program with minimal extra effort on the part of the chemist. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560851
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  • 5
    Electronic Resource
    Electronic Resource
    Density matrix of crystalline systems. II. The influence of structural and computational parameters (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 419-433 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-electron density matrix (DM) of a number of crystalline systems - lithium, graphite, boron nitride, silicon, and beryllium - are considered here, as resulting from Hartree-Fock-SCF-LCAO calculations. The influence of structural and computational parameters is discussed. It is shown in particular why the structure of chemical bonds in semiconductors leads to an oscillating long-range behavior of the DM, similar to that observed in metals, where these oscillations are related to the very existence of a Fermi surface. Concerning computational parameters, the influence of the density of sampling k points and of basis set on the calculated DM is considered; it is shown that the choice of the basis set is not a very critical one as far as the DM range is concerned. Some critical aspects of the interrelation between DM range and exchange part of the Fock Hamiltonian are analyzed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380305
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  • 6
    Electronic Resource
    Electronic Resource
    Density matrix of crystalline systems. I. Long-range behavior and related computational problems (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 395-417 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-electron density matrix (DM) of crystalline systems is discussed, especially concerning its longrange behavior; reference is made throughout to systems treated at a Hartree-Fock-LCAO-SCF level of approximation. The analysis is performed on the assumption of generally smooth behavior of eigenvalues and eigenvectors in k (reciprocal) space, so that they can be expressed by means of a truncated Fourier expansion. This assumption allows us to obtain analytic approximations for the DM, on the basis of the information collected at a few, suitably selected sampling k points. It is therefore possible at the same time to discuss the influence of structural parameters (dimensionality of the system, existence and shape of the Fermi surface, structure of the chemical bonds) and to set up a computational scheme that is general and simple enough.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380304
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