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  • Atomic, Molecular and Optical Physics  (3)
  • Electronic properties  (1)
  • cluster group  (1)
  • 1
    Digitale Medien
    Digitale Medien
    The band structures and magnetic properties of some transition-metal monophosphides I. Scandium phosphide (1981)
    Springer
    Theoretical chemistry accounts 59 (1981), S. 555-568 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Band Structure ; Binary phosphides ; Electronic properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract An improved method is described for the calculation of the band structures and density of states for three-dimensional solids. It is based on an LCAO-TB method. The method is applied to the scandium phosphide crystal. This material is calculated to be a semiconductor with a small band gap.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00552849
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  • 2
    Digitale Medien
    Digitale Medien
    Application of localized molecular orbitals to the solution of semiempirical self-consistent field equations (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 133-146 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: When conventional matrix algebra is used to solve the semiempirical self-consistent field equations for large systems, the time required rises as the third power of the size of the system. A consequence of this is that self-consistent calculations of large systems such as enzymes are impractical. By using localized molecular orbitals instead of matrix methods, the time required for these systems can be made almost proportional to the size of the system. In partial geometry optimizations, the time required depends only upon the size of the fragment being optimized and is almost independent of the size of the whole system. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Structure and electronic structure of polyacene (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 305-313 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: It is shown that infinite long polyacene chains may have three energetically close but structurally distinct isomers (a symmetrical, sym, form and two lower symmetry forms: one with double bonds in a trans and another isomer with double bonds in a cis pattern). The energetics is based on solid state MNDO theory. We discuss that the symmetrical form has a substantial energy gap Eg in the Hartree-Fock approach owing to exact exchange terms, which are nonlocal. Broken symmetry Hartree-Fock (HF) solutions for polyacene are also described. An angularly distorted structure suggested earlier on Jahn-Teller grounds is found to be energetically not favorable.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560350207
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  • 4
    Digitale Medien
    Digitale Medien
    Calculation of polymer elastic moduli using semiempirical methods (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 529-540 
    Details
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Extensional elastic moduli have been calculated for several organic high polymers based on the modified neglect of diatomic overlap (MNDO) Hamiltonian. Standard semiempirical methods, by application of the Born-von Karman boundary conditions, can be used to calculate heats of formation of polymer chain sections, or computational unit cells, called clusters. Unit cell heats of formation at elongated translation vectors, combined with experimental or estimated densities, allow for the calculation of elastic moduli. Two potential sources of error were identified: (a) finite geometry optimization can result in pseudorandom errors in the calculated heat of formation, and (b) anharmonic distortion can become significant at large strains. Errors due to both causes can typically be minimized if strains between 3 and 10% are selected. As expected, the calculated moduli, although higher than those observed experimentally, agree with longitudinal values for perfectly oriented systems.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/qua.560300746
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  • 5
    Digitale Medien
    Digitale Medien
    Symmetry groups for unit cells in solids (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 168-180 
    Details
    ISSN: 0192-8651
    Schlagwort(e): symmetry theory ; group theory ; point group ; space group ; cluster group ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Informatik
    Notizen: Two types of symmetry groups are commonly used in chemistry. Point groups are used for molecules, whereas, for solids, the 230 space groups are used. Neither of these types of symmetry groups are suitable for representing unit cells in solids, the symmetry of which is intermediate between that of point groups and space groups. To represent the symmetry of unit cells in an infinite lattice, a third type of symmetry group must be used. An algorithmic method of generating these symmetry groups is described. It can be demonstrated that these groups are valid by use of conventional symmetry group theory. This technique has been applied to the two-dimensional graphite lattice. Because the new method generates symmetry tables using only the topology of the system, the symmetry properties of graphs can also readily be derived. Last, the relationship between these groups and the other two types of groups is identified.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 168-180, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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