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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical study of the formation of closed curved graphite-like structures during annealing of diamond surface (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 863-870 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In recent high resolution transmission electron microscopic studies we have found that high temperature vacuum annealing (1200–1800 K) of ultradispersed (2–5 nm) and micron size diamond produces fullerene-like graphitic species, namely, onion-like carbon and closed curved graphite structures (multilayer nanotubes and nanofolds), respectively. Here we undertake theoretical studies to help in the understanding of the experimental data for these systems. (1) Calculations of cluster models by a standard semiempirical method (MNDO a software package) are used to explain the preferential exfoliation of {111} planes over other low index diamond planes. (2) The same approach suggests the likelihood that the graphitization is initiated by a significant thermal displacement of a single carbon atom at temperatures close to the Debye temperature. (3) At the diamond–graphite interface we have observed the formation of two curved graphitic sheets from three diamond {111} planes. We suggest that the evolution of this interface proceeds by a "zipper"-like migration mechanism with the carbon atoms of the middle diamond layer being distributed equally between the two growing graphitic sheets. (4) The observed mosaic packaging of closed curved graphite structures during the diamond surface graphitization is suggested to be a self-assembling process. This process is explained in terms of the "stretching" of a bowed graphite hexagonal network. The stretch is due to the fact that, if relaxed, the network would be smaller than the initially transformed hexagonal diamond (111), and to the increased separation between the separated sheet and the surface. The initial phase of the process is studied quantitatively using a molecular mechanics simulation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370816
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  • 2
    Electronic Resource
    Electronic Resource
    Hydrogen activation on copper catalytic sites in stereoselective alkyne hydrogenation (1995)
    Springer
    Reaction kinetics and catalysis letters 56 (1995), S. 77-86 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The interaction of hydrogen with copper clusters has been studied using EHM/AP method (extended Hückel method with Anderson's potential). Copper atoms are shown to form a dihydride structure with a high stability, which is due to the low mobility of atomic hydrogen on the surface. The formation of this complex appears to be favorable for concerted hydrogenation of acetylenes tocis-olefins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02066953
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  • 3
    Electronic Resource
    Electronic Resource
    On some ways of modifying semiempirical quantum chemical methods (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 58 (1996), S. 175-184 
    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 problems of semiempirical quantum chemical calculations of (a) spin densities in paramagnetic organometallics, (b) hydrogen bonds, and (c) bond energies and the structure of transition-metal compounds are discussed. Some modifications of the existing semiempirical quantum chemical method are presented. An extended NDDO approximation has been developed. This scheme includes explicit symmetric orthogonalization of the core Hamiltonian and the use of Hellmann's effective core potential for core-electron interaction. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    The evaluation of the hybrid one-center integrals used in the semiempirical NDDO-type methods for d-elements from spectra (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 439-444 
    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: For semiempirical SCF MO methods based on the NDDO assumption, the so-called one-center hybrid integrals of the type (ab/cd) are required. These integrals are expressed in terms of the Slater-Condon parameters (SCP) Rk(abcd) with different radial functions. The SCPs from atomic spectra are evaluated by taking into account configurational interaction (CI). As an example, the R1(sdpp), R2(sdpp), and R2(sddd) SCPs for Ti I, Ti II, and Ti III have been evaluated and the values of these parameters are compared with those calculated with Slater-type orbitals.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560420306
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