Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session J3: Condensed Matter: Electronic Structure |
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Chair: Barry Zink, University of Denver Room: Union East, 3rd Floor Ray |
Saturday, October 18, 2008 1:30PM - 1:42PM |
J3.00001: Electronic structure of novel semiconducting nanotubes Peter Lyon, Bret Hess Since their discovery, nanotubes have attracted much interest because of their potential usefulness in many areas of science and technology. Although carbon nanotubes have received most of that attention, new types of nanotubes with similar structure have recently been studied. A family of nitride nanotubes, including boron-nitride, aluminum-nitride, and gallium-nitride have been predicted theoretically and some have been created in the laboratory. We are investigating the stability and electronic structure of gallium phosphide and gallium arsenide nanotubes using density functional theory. [Preview Abstract] |
Saturday, October 18, 2008 1:42PM - 1:54PM |
J3.00002: Electronic Structure Calculations of NiTi Based Ternary Systems Henry Schreiner, III, Jung-Hwan Song, Nicholas Hatcher, Arthur J. Freeman In this study, the electronic structures of ternary nickel titanium ``shape memory'' alloys were investigated using a first principles approach within density functional theory. We used the full potential linearized augmented plane wave (FLAPW) method for all calculations, and developed models of the alloys NiTiCu, NiTiFe, and NiTiPd. Both the B2 and the B19' phases for these systems were modeled to determine phase energetics and fundamental mechanisms for structural preference. Splitting of Ni d-states due to Cu and Pd additions and total energy comparisons of the phases explain the effect of ternary additions on changing martensitic transition temperatures. Total energy analysis was used to predict the ground state phase change of NiTiCu B19' to B19 as Cu content increases from 12 at{\%} to 25 at{\%}, which is consistent with recent experiments. Site preferences for Cu and Fe were investigated for same composition alloys. From these results and by predicting alloy properties from first principles, we show how these ab initio calculation methods may be used for designing novel materials. [Preview Abstract] |
Saturday, October 18, 2008 1:54PM - 2:06PM |
J3.00003: B2 decomposition of X5Al (X=Sc, Ti, V, Cr, Y, Zr, Nb, and Mo) system, A First-Principles Study Payam Norouzzadeh, Mahdi Sanati The phase stability of B2 X5Al (X=Sc, Ti, V, Cr, Y, Zr, Nb, and Mo), and slightly rearranged atomic structures are examined by first-principles calculations. The ground state energy calculations show instability against the omega structure type atomic displacement in all of these systems. We use electronic density of states~ and a rigid band modeling to understand and explain the electronic origin of the stability of each system. In order to estimate the strength of each bond, the heats of formation for several compounds are calculated. We find that the strength of the transition metal (TM)-Al bond increases from Sc to Cr, and Y to Mo. The crystal structure parameters, such as lattice constants and bulk modulus, are calculated. [Preview Abstract] |
Saturday, October 18, 2008 2:06PM - 2:18PM |
J3.00004: Phase transformation of 2$H$ and 6$H$-SiC at high pressure: An ab initio constant pressure study Murat Durandurdu, Sitki Eker We study the pressure-induced phase transition in the 2H-SiC (wurtzite) and 6H-SiC crystals using a constant pressure \textit{ab initio} technique. A first order phase transition to a rocksalt structure in both SiC polytypes is predicted in the constant pressure simulations. The transformation in 2H-SiC consists of two successive processes. First the 2H-SiC crystal transforms into a fivefold coordinated hexagonal structure with space group $P6_{3}$\textit{/mmc} due to a compression in the direction of the $c$-axis. Second the hexagonal phase becomes unstable in respect to shear deformation and converts to first a fivefold coordinated orthorhombic intermediate state within the \textit{Cmcm} symmetry, and then a rocksalt state. The phase change in 6H-SiC also proceeds in two stages: 6H-SiC is first compressed along the c-direction and then it undergoes a shear deformation on the $a-b$ planes. This transformation mechanism is quite similar to that of the 2H-SiC-to-rocksalt observed but there is no metastable phase identified along this path. We also study the 2H-to-rocksalt, zinc blende-to-rocksalt and 6H-to-rocksalt phase transformations of SiC from the enthalpy calculations and find that all SiC polytypes show nearly similar equation of state and transforms to a rocksalt structure about 100.0 GPa, in excellent agreement with experiments. [Preview Abstract] |
Saturday, October 18, 2008 2:18PM - 2:30PM |
J3.00005: Pressure-induced phase transformation SnO$_{2}$: An ab initio constant pressure study Daniel Yehdego, Murat Durandurdu We study the behavior of SnO$_{2}$ under rapid hydrostatic pressures using constant-pressure ab initio simulations. We find that the rutile-type SnO$_{2}$ transforms into the CaCl$_{2}$-type structure. At a high pressure of about 20 GPa, a phase transformation into a cubic fluorite-type structure is observed. The orthorhombic Pnma cotunnite-structured phase is formed above 100 GPa. The transformation mechanisms at the atomistic level are discussed. [Preview Abstract] |
Saturday, October 18, 2008 2:30PM - 2:42PM |
J3.00006: Study of the structural and spectroscopic properties of Zn based clusters by density functional theory Venkata Chaganti, Rajendra Zope, Tunna Baruah ZnS, ZnSe, and ZnTe in the solid phase are semiconductors and have been extensively studied for their possible applications in semiconducting industry. The small clusters (aggregates of atoms containing a few tens of atoms) of semiconductors and metals often adopt very different shapes than the fragments of these materials in the bulk phase. The present work is devoted to understanding the structural and electronic properties of small clusters of the zinc based semiconductors with particular focus on the clusters of ZnS. The equilibrium structures of clusters are obtained by local optimization (conjugate gradient) by starting with several possible atomic configurations. The calculations are performed using advanced electronic structure package called NRLMOL. This package uses density functional theory. The calculations are free from pesudopotential approximation i.e. both valences as well as core electrons are explicitly treated in calculations. The nature of each local minimum (structure) is analyzed by computing the vibrational frequencies within the harmonic approximation. The electronic properties such as ionization energies, the band gap (HOMO-LUMO gap), and electron affinity are obtained for all stable structures. Additionally, spectroscopic properties such as infra-red and Raman spectra are obtained which will be helpful in possible detection and identification of these clusters in experiment.~ The evolutions~of all these properties are studied as a function of the size of clusters. [Preview Abstract] |
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