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  • Computational Chemistry and Molecular Modeling  (2)
  • porphyrinoids
  • Bischlorine
  • McMurry-Reaktion
  • 1990-1994  (2)
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  • 1
    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: Ab initio Hartree-Fock band structure calculations are presented for the first time for lithium phosphide (Li3P) and lithium arsenide (Li3As) in the hexagonal P6/mmm crystal structure. Results are compared to those for lithium nitride (Li3N). The new calculations for Li3N agree with previous Hartree-Fock calculations, except for the valence band structure where results of previous pseudopotential calculations are confirmed. Geometry optimization for Li3P yields a lattice parameter a of 4.45 Å and a c value of 4.80 Å. These values differ markedly from experimental results reported to be 4.271 and 7.590 Å, respectively. A similar discrepancy is found for lithium arsenide: a = 4.60 Å and c = 4.96 Å have to be compared to the reported experimental values of 4.397 Å for a and 7.824 Å for c. Force constants are derived for in-plane and interplane vibrations. The band structures for Li3P and Li3As are found to be very similar to the one calculated for Li3N. Using Li3P as an example, it is shown how the band structure of the insulator can be derived from the band structures of the two metallic constitutent Li2P and Li monolayers. The metal-insulator transition occurs if the inter-plane distance falls below 4.25 Å. Contrary to expectations raised earlier, it is found that the 3d electrons in arsenic are strongly localized, evidenced by a very narrow d band width of 0.1 eV. They cannot be used to explain the difference in conductivity between the phosphide and the arsenide. A Mulliken population analysis gives charge distributions close to the ideal ionic structure (Li+)3X3-, X = N, P, and As. Overall it is found that hexagonal lithium phosphide and lithium arsenide arsenide are more similar to lithium nitride and less anisotropic than suggested previously. This discrepancy could be due to the use of polycrystalline samples in earlier experiments.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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: Unrestricted Hartree-Fock calcuations coupled with second-order Møller-Plesset correlation correction were performed to study the structures and energetics of microlusters. For (BN)2, linear and rhombus forms are almost isoenergetic, whereas cyclic forms are preferable for (BN)3 and (BN)4 clusters. As a general trend, linear isomers prefer the triplet spin state, whereas cyclic isomers prefer the singlet spin state. Total charge density plots show a strong dominace of the B—N bond, indicating that the extent of its polar character becomes stronger with the increase in the cluster size. The loss of a BN monomer is shown to be the most likely fragmentation channel for both neutral and single-ionized clusters. We find that neutral (BN)n clusters have the same structural configurations as those of their corresponding C2n counterparts. This similarity follows the isoelectronic principle and is of importance due to recent interest in the investigations of BN fullerene analogs. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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