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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4428-4434 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An isotropic compression of both the perfect solid cyclotrimethylene trinitramine (C3H6N6O6), also known as RDX, and of the solid containing vacancies is simulated using the ab initio Hartree–Fock method combined with two different crystal models: a periodic (band structure) and a molecular cluster. We show that an external pressure causes a significant decrease of the optical gap for both the perfect material and the crystal with vacancies. The solid RDX is found to be highly compressible; a pure crystal could be compressed to 57% of its equilibrium volume, whereas crystals containing vacancies are even more compressible. The critical pressure necessary for the insulator–metal transition is also predicted. It is shown that the voids present in a real RDX solid lower the metallization pressure by about 30%. Theoretical results are in close agreement with the experimental data on solid and porous RDX. The influence of defects present in the crystal and the relation to control of the sensitivity to detonation are discussed in detail. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4962-4970 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An attempt to model the electronic structure of molecular crystals containing an edge dislocation at the ab initio Hartree–Fock level is performed. The experimentally determined configurations for edge-type dislocations with the Burgers vector [001] in crystalline cyclotrimethylene trinitramine (RDX) and pentaetythritol tetranitrate (PETN) are theoretically simulated. It is shown that a shear stress, induced by the dislocations, produces local electronic states in the fundamental band gap of the crystal. These states are mainly formed by molecular orbitals of critical bonds (which are the N–NO2 group in RDX and the O–NO2 group in PETN) responsible for the stability of the materials. Optical absorption attributed to these electronic states is predicted and compared to the available experimental data. Properties of the defective solids are compared with those of the perfect crystals. Correlation of the electronic structure and sensitivity of the materials to initiation of a chemical reaction as well as some practical applications of the obtained results are discussed. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2215-2218 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effect of a hydrostatic compression on the electronic structure of cyclotrimethylene trinitramine (C3H6N6O6), also known as RDX, with an edge dislocation has been studied by means of the ab initio Hartree–Fock method for a periodic system combined with the many-body perturbation theory. An external pressure causes a significant decrease of the optical gap for both the perfect material and the crystal with dislocations. The edge dislocations produce local electronic states in the optical gap whereas the external pressure moves these states deep within the band gap. This contributes strongly to properties of the RDX crystals creating favorable conditions for the N–NO2 chemical bond rupture due to exciton formation. The relationship between the edge dislocations, hot spot formation, and the sensitivity of RDX to detonation are discussed in detail. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4783-4792 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report ab initio molecular orbital calculations on neutral and single-ionized stoichiometric clusters of MgO containing up to 26 atoms. Geometrical parameters of the neutral clusters are optimized at the Hartree–Fock level, whereas for the ionized clusters we have applied the vertical approximation. Correlation corrections in the clusters with 2–12 atoms are included at the equilibrium geometries by means of second order Moller–Plesset calculations. We have found that the structures based on the (MgO)3 subunit are preferred in comparison to cubelike configurations, although the energy difference decreases with the increase in cluster size. The relative stability of neutral and single-ionized clusters has been studied by means of the fragmentation path involving the loss of a neutral MgO molecule. The calculated "magic numbers'' for the charged clusters, (MgO)n+, are in complete agreement with the abundance maxima observed in the mass spectra. Finally, we explore the size dependence of structural, energetic, and electronic properties. These properties show a large variation from the monomer to the (three-dimensional) eight atom cluster, followed by a softer approach towards the corresponding bulk limit.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 63 (1997), S. 615-621 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solid energetic substances have long played an important technological role as explosives, as well as for fuels. In this article, the authors concentrate on a type of explosive considered a primary explosive, lead azide, and its related compounds, lithium azide and sodium azide. Recent interest in more fundamental questions relating to the basic properties of these systems as materials, coupled with a desire to probe fundamental questions relating to the initiation and sustaining of the chemical reactions leading to combustion/detonation, is generating significant interest in the basic solid-state properties of such energetic systems. In particular, recent analysis of detonation by Gilman emphasizes the need to include excitation of the electronic system in obtaining an understanding. In this article, the band structures of the three solid metal azides are studied. This is done for both the normal lattice geometry and also in isotropically compressed geometries. These studies found that the alkali azide band gaps are far wider than is the lead azide gap and the lead azide gap is far more sensitive to narrowing with lattice compression than are the gaps for the alkali azides. In fact, the gap for sodium azide is found to widen with compression rather than narrow. The authors found that there is much seen in the band structures of these azides to lend some support to the Gilman model and also to demonstrate the importance of solid-state effects on the electronic structure and possible behavior of such energetic systems. © 1997 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 607-619 
    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 use of finite clusters of atoms to represent the physically interesting portion of a condensed matter system has been an accepted technique for the past two decades. Physical systems have been studied in this way using both density functional and Hartree-Fock methodologies, as well as a variety of empirical or semiempirical techniques. In this article, the author concentrates on the Hartree-Fock based methods. The attempt here is to construct a theoretical basis for the inclusion of correlation corrections in such an approach, as well as a strategy by which the limits of a finite cluster may be transcended in such a study. The initial appeal will be to a modeling approach, but methods to convert the model to a self-contained theory will be described. It will be seen for the case of diffusion of large ions in solids that such an approach is quite useful. A further study of the case of adsorption of rare gas atoms on simple metals will demonstrate the value of inclusion of electron correlation.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 1980-09-15
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 8
    Publication Date: 1971-09-20
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 9
    Publication Date: 1973-09-17
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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  • 10
    Publication Date: 1971-08-30
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
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