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1.
Summary Assuming a completely disordered lattice it is shown that all the states are localized when the disorder parameterx=a
0/0 reachesthe value 0.31, wherea is the mean atomic separation anda
0 is the Bohr radius. 相似文献
2.
Pierre Devillard 《Journal of statistical physics》1991,62(1-2):373-387
In the quantum transport problem of a tight-binding Anderson model, the statistics of eigenvalues for the transfer matrices of thin disordered slabs is studied. Numerical simulations indicate that the probability distribution of nearest neighbor eigenvalue spacing and the
3 statistics have already become close to that of the Gaussian orthogonal ensemble for sample lengths of the order of the mean free path, provided that transverse localization effects are not important. An intuitive argument is given why this should occur independently of the size of the matrix. Therefore, good mixing of the channels is not essential for obtaining Gaussian orthogonal ensemble type statistics and universal conductance fluctuations. 相似文献
3.
Xavier Fradera Jordi Poater Sílvia Simon Miquel Duran Miquel Solà 《Theoretical chemistry accounts》2002,108(4):214-224
This article presents an overview of recent advances in the study of electron pairing through the use of localization and
delocalization indices obtained from double integration over atomic basins of the exchange–correlation density in the framework
of the atoms-in-molecules theory. These localization and delocalization indices describe the intra- and interatomic distribution
of the electron pairs in a molecule. The main results of the application of these second-order indices to the analysis of
molecular structure and chemical reactivity are briefly reviewed. It is shown that localization and delocalization indices
represent a powerful tool to describe the electron-pair structure of molecules, which, in turn, provides deeper insight into
relevant chemical phenomena such as electron correlation effects and the formation of localized α, β electron pairs.
Received: 8 April 2002 / Accepted: 26 June 2002 / Published online: 6 September 2002
Acknowledgements. Financial help was furnished by the Spanish DGES projects no. PB98-0457-C02-01 and BQU2002-04112-C02-02. J.P. thanks the
Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for benefiting from a doctoral
fellowship, no. 2000FI-00582. M.S. is indebted to the Departament d'Universitats, Recerca i Societat de la Informació of the
Generalitat de Catalunya for financial support through the Distinguished University Research Promotion, 2001. We also thank
the Centre de Supercomputació de Catalunya for providing us with computing facilities.
Correspondence to: M. Solà e-mail: miquel.sola@udg.es 相似文献
4.
Vinzenz Bachler 《Theoretical chemistry accounts》1997,96(4):223-242
A straightforward procedure is proposed for expanding a molecular orbital determinantal wave function into a set of determinantal
wave functions composed of atomic orbitals localized at the atoms of a molecule. By employing this method, atomic orbital
determinants and their weights can be derived for a molecule from the computed molecular-orbital wave function. The procedure
permits the interpretation of a molecular orbital determinantal wave function in terms of bonding schemes related to the classic
resonance structures used by organic chemists. By using the unrestricted molecular orbital determinant, bonding schemes and
their weights are obtained for butadiene, the butadiene radical cation and the acrylonitrile radical anion. Their dominant
bonding schemes are in accord with the relevant resonance structures for these molecules. For the butadiene radical cation
and the acrylonitrile anion they are shown to be compatible with the accepted mechanisms of the electrochemical coupling reactions
of butadiene and acrylonitrile.
Received: 7 August 1996 / Accepted: 18 March 1997 相似文献
5.
BiGaIn2S6 – Synthesis, Structure, and Properties The novel compound BiGaIn2S6 was obtained in the quaternary system Bi–Ga–In–S. BiGaIn2S6 forms red transparent platelets and exhibits a range of homogeneity between BiGa1In2S6 and BiGa0.8In2.2S6. The compound is a semiconductor with Eg(opt.) = 1.9 eV. – BiGaIn2S6 crystallizes monoclinically forming a new structure type (a = 1112.0 pm, b = 380.6 pm, c = 1228.0 pm, β = 116.30°, Z = 2, space group P21/m, no. 11). The S atoms form strongly corrugated 2 D fragments of the (hc)2 sphere packing type. The In atoms occupy octahedral holes (d(In–S) = 262 pm) and the Ga atoms tetrahedral holes (d(Ga–S) = 234 pm) inside the 2 D-layers. The Bi atoms on the top of trigonal BiS3 pyramids (d(Bi–S) = 265 pm) are at the periphery of the layers and have four additional S ligands from the neigbouring layer at much larger distances (d(Bi–S) = 319 pm). – The bonding of a BiIII sulfide is analyzed for the first time by the Electron Localization Function (ELF). 相似文献
6.
7.
Of interest here is the influence of loading rate on the stability of structures where inertia is taken into account, with particular attention to the comparison between static and dynamic buckling. This work shows the importance of studying stability via perturbations of the initial conditions, since a finite velocity governs the propagation of disturbances. The method of modal analysis that determines the fastest growing wavelength, currently used in the literature to analyze dynamic stability problems, is meaningful only for cases where the velocity of the perfect structure is significantly lower than the associated wave propagation speeds. 相似文献
8.
An asymmetric double-well potential is considered, assuming that the wells are parabolic around the minima. The WKB wave function of a given energy is constructed inside the barrier between the wells. By matching the WKB function to the exact wave functions of the parabolic wells on both sides of the barrier, for two almost degenerate states, we find a quantization condition for the energy levels which reproduces the known energy splitting formula between the two states. For the other low-lying non-degenerate states, we show that the eigenfunction should be primarily localized in one of the wells with negligible magnitude in the other. Using Dekker’s method (Dekker, 1987), the present analysis generalizes earlier results for weakly biased double-well potentials to systems with arbitrary asymmetry. 相似文献
9.
Dr. Bing Wang Dr. De Yu Wang Dr. Zhenxiang Cheng Prof. Dr. Xiaolin Wang Prof. Dr. Yuan Xu Wang 《Chemphyschem》2013,14(6):1245-1255
Phase stability is important to the application of materials. By first‐principles calculations, we establish the phase stability of chromium borides with various stoichiometries. Moreover, the phases of CrB3 and CrB4 have been predicted by using a newly developed particle swarm optimization (PSO) algorithm. Formation enthalpy–pressure diagrams reveal that the MoB‐type structure is more energetically favorable than the TiI‐type structure for CrB. For CrB2, the WB2‐type structure is preferred at zero pressure. The predicted new phase of CrB3 belongs to the hexagonal P‐6m2 space group and it transforms into an orthorhombic phase as the pressure exceeds 93 GPa. The predicted CrB4 (space group: Pnnm) phase is more energetically favorable than the previously proposed Immm structure. The mechanical and thermodynamic stabilities of predicted CrB3 and CrB4 are verified by the calculated elastic constants and formation enthalpies. The full phonon dispersion calculations confirm the dynamic stability of WB2‐type CrB2 and predicted CrB3. The large shear moduli, large Young’s moduli, low Poisson ratios, and low bulk and shear modulus ratios of CrB4? PSC and CrB4? PSD indicate that they are potential hard materials. Analyses of Debye temperature, electronic localization function, and electronic structure provide further understanding of the chemical and physical properties of these borides. 相似文献
10.
Nanoscale resolution in material sciences is usually restricted to scanning electron beam microscopes. Here we present a procedure that allows single molecule resolution of the sample surface with visible light. Highlighting the performance we used electron beam lithography to generate highly regular nanostructures consisting of interconnected cubes. The samples were labeled with Alexa 647 dyes. The spatial organization of the dyes on nanostructured surfaces was localized with single molecule resolution using localization microscopy. This succeeded also in an absolute spatial calibration of the localization method applied (spectral precision distance microscopy/SPDM). The findings will contribute to the field of product control for industrial applications and long-term fluorescence imaging. 相似文献