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  • 1
    Electronic Resource
    Electronic Resource
    First-principles calculation of the conformation and electronic structure of polyparaphenylene (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9623-9631 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this article, an all-electron first-principles total energy calculation with Gaussian-type functions for the wave functions, for the exchange correlation potential, and for the charge density has been applied for single chains of polyparaphenylene (PPP). A local-density approximation within a helical band structure approach has been used. The calculated torsional potential shows a minimum at the torsion angle of 34.8°. The internal coordinates were optimized in the equilibrium conformation and are in good agreement with experimental and other theoretical results. The calculated direct band gap is 2.54 eV compared with the experimental result from UPS spectra of 3.4 eV for the gas phase. The band structure strongly depends on the conformation which suggests that the electronic properties can be modified in a wide range through doping or addition of side groups. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477624
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  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of the even wave functions of the hydrogen atom in the path-integral formalism
    Amsterdam : Elsevier
    Physica 64 (1973), S. 47-62 
    Details
    ISSN: 0031-8914
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-8914(73)90113-4
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  • 3
    Electronic Resource
    Electronic Resource
    An LDA calculation of the conformation and electronic structure of polytetrafluoroethylene (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 64 (1997), S. 243-246 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density functional calculation of the structural and electronic properties of polytetrafluoroethylene systems with several different dihedral angles is presented using two different local density approximations, the Gáspár-Kohn-Sham and the Perdew-Zunger. All the geometrical parameters were optimized simultaneously for the stable conformation. The torsional potential curve shows an absolute minimum at the dihedral angle of 163.7°, corresponding to a slightly deformed planar zigzag conformation. Other two distinct local minima for the quasi-stable helical conformation are found at the gauche form. The calculated valence and conduction bands are discussed and compared with other theoretical calculations and experiment.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 243-246, 1997
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Self-consistent second-order screening in many-body theory (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 51 (1994), S. 389-396 
    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: Self-consistent screening arises in all many-body problems where one-particle equations containing functionals of the solutions are considered. In the theory of simple metals, e.g., these one-particle equations are usually solved to second-order perturbation in the crystal pseudopotential and to first order in the screening. However, higher-order screening terms have a sizable effect on the form factors, the electron charge density, and the screened pseudopotential. The effects of second order are presented for the bcc simple metals Na and Ba. A nonlocal exchange-correlation potential has been used since local density approximations such as ρ1/3 cause difficulties in the electron-electron dielectric function. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560510606
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  • 5
    Electronic Resource
    Electronic Resource
    Total energy calculations in the DFT on binary compounds (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 339-345 
    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: Calculations are carried out using first-principles self-consistent local-density and nonlocal density theory of the electronic structure, the total energy, and the charge density of a variety of semiconducting and insulating compounds under hydrostatic and uniaxial pressure. For several cases, the transition pressure from one structure to another is determined as well as the pressure coefficients of the main band gaps. It is shown that several properties are calculated with adequate accuracy to be compared with experiment, so that values which have not yet been measured are trustworthy predictions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560550405
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational spectra of molecules in the Hartree-Fock dielectric screening approachWork supported by a research grant from the Sponsored Research Committee of Control Data Corporation, Minneapolis, Minnesota. (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 311-315 
    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: Traditionally, the calculation of the vibrational spectra of molecules involves at one point or another a numerical differentiation procedure. Such a method has some serious drawbacks both in efficiency and in accuracy. In this paper, an alternative method based on linear response theory is presented. The second derivative of the ground-state energy is expressed in terms of the electron density response matrix by means of perturbation theory. The unperturbed wave functions are obtained from the Hartree-Fock equation. First-order perturbation theory applied to this equation leads to the Hartree-Fock linear response. As an illustration of this method the vibrational frequency of a H2 molecule is calculated. The result is 1.348 × 1014 Hz as compared to the experimental value of 1.319 × 1014 Hz. This method is also applicable in the calculation of the phonon dispersion curves of solids.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180144
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  • 7
    Electronic Resource
    Electronic Resource
    Moment expansion method to calculate vibrational frequencies of molecules and solids (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 317-321 
    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 vibrational properties of a quantum system are determined by the density response matrix. In linear response theory this quantity is connected to the polarizability matrix, which can be expressed in terms of a double summation over one-particle energies and wave functions. In has been shown that this expression is not useful in the calculation of vibrational frequencies because of the very slow convergence of the summation in terms of the unoccupied states. In this paper, a different but equivalent expression is presented using a continued fraction. The resulting expression contains only one summation over the occupied states, solving in this way all the problems connected with the sum-over-states expression of the polarizability matrix. The elimination of all the unoccupied states via the use of the moment formula turns out to be a crucial step in the solution of the problem of the first-principles calculation of the vibrational spectra of molecules and solids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180145
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  • 8
    Electronic Resource
    Electronic Resource
    Microscopic theory of the average band gap of semiconductorsWork supported by a research grant of the Sponsored Research Committee of Control Data Corporation, Minneapolis, Minnesota. (1980)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 18 (1980), S. 615-618 
    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: In Phillips' spectroscopic theory of semiconductors, the covalency and ionicity are derived empirically from the average band gap between the highest valence and lowest conduction bands. In this paper an explicit expression for the average band gap is derived based on a continued fraction representation of the polarizability matrix. Results of a calculation for six covalent and polar semiconductors, using the pseudopotential model, are presented and compare favorably with experimental values.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560180235
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