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Yong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • exact two component relativistic Energy Band Theory and application
    Journal of Chemical Physics, 2016
    Co-Authors: Rundong Zhao, Yong Zhang, Yunlong Xiao
    Abstract:

    An exact two-component (X2C) relativistic density functional Theory in terms of atom-centered basis functions is proposed for relativistic calculations of Band structures and structural properties of periodic systems containing heavy elements. Due to finite radial extensions of the local basis functions, the periodic calculation is very much the same as a molecular calculation, except only for an Ewald summation for the Coulomb potential of fluctuating periodic monopoles. For comparison, the nonrelativistic and spin-free X2C counterparts are also implemented in parallel. As a first and pilot application, the Band gaps, lattice constants, cohesive energies, and bulk moduli of AgX (X = Cl, Br, I) are calculated to compare with other theoretical results.

  • a novel approach to calculation of the second order nonlinear optical susceptibilities of organic crystals based on Energy Band Theory
    Principles and Practice of Constraint Programming, 2000
    Co-Authors: Yong Zhang
    Abstract:

    Abstract The second-order nonlinear optical susceptibilities in five organic crystals are studied based on the EHMO Band-structure method. The crystals studied included m -aminophenol, urea, m -dinitrobenzene, POM [3-methyl-4-nitropyridine-1-oxide] and m -nitroaniline. The β cell tensor components for a unit cell of crystals are calculated by the sum-over-states method. Results are presented for the density of states and second-order nonlinear optical coefficients d (2) (0), which are compared with other existing calculations and experimental data. The overall agreement of our calculations with available data is quite satisfactory. Moreover, the effect of the interactions between neighboring unit cells on the hyperpolarizability tensor components of β cell is examined and analyzed. The results show that the procedure developed in this work provides a new insight into the second-order susceptibilities of organic molecular crystals, which is important in molecular engineering.

Hugo F Franzen - One of the best experts on this subject based on the ideXlab platform.

  • the structural phase transition in calcium aluminum compound caal4 a concerted application of landau Theory and Energy Band Theory
    Journal of the American Chemical Society, 1993
    Co-Authors: Gordon J Miller, Fan Li, Hugo F Franzen
    Abstract:

    CaAl[sub 4] undergoes a reversible, structural transformation at 170[degrees]C according to high-temperature X-ray powder diffraction experiments. The high-temperature phase adopts the tetragonal BaAl[sub 4] structure (space group I4/mmm), while the low-temperature phase is monoclinic, C2/m, with lattice parameters, a = 6.1526 (15) [angstrom], b = 6.1730 (13) [angstrom], c = 6.3290 (14) [angstrom], [beta] = 118.026 (16). The Landau Theory of phase transitions correctly provided a structural model for the low-temperature phase, which could be subsequently refined. Also, electronic structure calculations on both forms of CaAl[sub 4] allow rationalization of the transformation in terms of changes in local chemical bonding within the Al framework. 26 refs., 8 figs., 8 tabs.

Yang Lu-zhao - One of the best experts on this subject based on the ideXlab platform.

  • variational Energy Band Theory for polarons mapping polaron structure with the global local method
    Journal of Chemical Physics, 1997
    Co-Authors: David W Brown, Katja Lindenberg, Yang Lu-zhao
    Abstract:

    In this article we revisit from a contemporary perspective a classic problem of polaron Theory in one space dimension following the variational approach originally taken by Toyozawa. Polaron structure is represented by variational surfaces giving the optimal values of the complete set of exciton and phonon amplitudes for every value of the joint exciton-phonon crystal momentum κ. Through this exfoliation of the exciton-phonon correlations comprising the polaron, characteristic small polaron, large polaron, and nearly free phonon structures are identified, and the manner in which these compete and/or coexist is examined in detail. Through such examination, the parameter space of the problem is mapped, with particular attention given to problematic areas such as the highly quantum mechanical weak-coupling regime, the highly nonlinear intermediate-coupling regime, and to the self-trapping transition that may be said to mark the onset of the strong-coupling regime. Through such examination of the complete par...

Ouyang Zhongcan - One of the best experts on this subject based on the ideXlab platform.

  • strain Energy and young s modulus of single wall carbon nanotubes calculated from electronic Energy Band Theory
    Physical Review B, 2000
    Co-Authors: Zhou Jianjun, Ouyang Zhongcan
    Abstract:

    The strain energies in straight and bent single-walled carbon nanotubes (SWNTs) are calculated by taking account of the total Energy of all the occupied Band electrons. The obtained results are in good agreement with previous theoretical studies and experimental observations. The Young's modulus and the effective wall thickness of SWNT are obtained from the bending strain energies of SWNTs with various cross-sectional radii. The repulsion potential between ions contributes the main part of the Young's modulus of SWNT. The wall thickness of SWNT comes completely from the overlap of electronic orbits, and is approximately of the extension of $\pi$ orbit of carbon atom. Both the Young's modulus and the wall thickness are independent of the radius and the helicity of SWNT, and insensitive to the fitting parameters. The results show that continuum elasticity Theory can serve well to describe the mechanical properties of SWNTs.

P. M. Marcus - One of the best experts on this subject based on the ideXlab platform.

  • chapter 2 Energy Band Theory of metallic magnetism in the elements
    Handbook of Magnetic Materials, 1993
    Co-Authors: V L Moruzzi, P. M. Marcus
    Abstract:

    Publisher Summary This chapter discusses the Energy Band Theory of metallic magnetism in the elements. Some of these magnetic phases are produced by epitaxial growth, which can expand a lattice, but the greatest number is found by application of the Band Theory of magnetism. This Theory has a sound basis and a computationally practicable form to obtain reliable ground-state properties of crystalline elemental solids. The Theory makes use of a set of Schrodinger-like one-electron equations to describe the ground state of a system with given nuclear positions. The equations contain an effective one-electron potential such as a function of electron position, which adds exchange and correlation effects to Hartree-type Coulomb terms to describe electron electron interactions. Several forms of the effective potential are deduced from various physical approximations; among these forms are the X α form based on a statistical treatment of the exchange interaction and the local-density approximation (LDA) in the density functional Theory of the ground state. The LDA results agree better with experiment and have a sounder physical basis, so that recent work is mostly with the LDA. The computation of ground-state magnetic properties by the augmented spherical wave method is described, including the procedure for locating magnetic phases and their stability limits. The useful simple Stoner formulation is given and related to the general Theory.