Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z42: Many Body II |
Hide Abstracts |
Sponsoring Units: DCOMP Chair: Eduardo Fradkin, University of Illinois at Urbana-Champaign Room: D138 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z42.00001: Test of Variational Procedures for Electronic Structure Studies by Comparison of Results for Energies of Atoms with Experiment and Results from Bruckner-Goldstone Many-Body Perturbation Theory --Neon Atom Archana Dubey, H. Paudel, R.H. Pink, S.R. Badu, R.H. Scheicher, T.P. Das During the latter half of the last century, great advances were made, through the Bruckner Goldstone Diagrammatic Many Body Perturbation Theory (BGMBPT), in accurate quantitative understanding of atomic properties. These investigations have provided a wealth of data which can now be used to test the accuracy of variational procedures in use currently for investigations of electronic structures and properties of multicenter systems like molecules and solid state systems. In the present talk, we shall consider neon atom where an earlier BGMBPT investigation [1] has provided excellent agreement with experiment for the total energy including correlation contributions. We have focused for this comparison on the Gaussian basis set based, first-principles Hartree-Fock procedure combined with Many Body Perturbation Theory, and the B3LYP procedure using DFT based exchange and correlation potentials, for neon. Results of our investigations will be presented and discussed.\\[4pt] [1] Taesul Lee, N.C. Dutta and T.P. Das, Phys. Rev. A4,1410(1971) [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z42.00002: Calculation of Correlation Functions using the Momentum Average Approximation Glen Goodvin, Mona Berciu The Momentum Average (MA) approximation has been successfully applied to a growing number of Hamiltonians involving electron-phonon (el-ph) coupling since its discovery only a few years ago. This analytical non-perturbative approximation is exact in both the zero bandwidth and zero el-ph coupling limits, and by summing all of diagrams in the full diagrammatical expansion of the self-energy, albeit with approximations made on each of them, it gives highly accurate results over the entire parameter space. In this work we explore another significant generalization of the approximation by using MA to calculate correlation functions, where the optical conductivity of the Holstein polaron is used as a specific example. A comparison of the MA results against available numerical data again displays a high degree of accuracy for very minimal computational effort. Based on our previous generalizations of MA to systems with momentum-dependent el-ph couplings, we argue that MA could be used to study the linear response of an even broader class of problems. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z42.00003: Exact solution to the random matrix problems from the symmetries of integrable systems Alex Vagov, Oleg Vorov The problem with random non-Hermitian Hamiltonian (the Hatano-Nelson problem) arises in context of theory of depinning of the flux lines from extended defects in type II superconductors subject to a tilted external magnetic field. It is also of great interest in the context of random matrix theories. We employ a novel method, based on the inverse scattering/spectral transform, to obtain an exact analytic solution to the matrix version of the Hatano-Nelson problem. The idea is to use the exact connection between the linear (spectral or scattering problem) and exactly integrable nonlinear systems. This allows us to evaluate exactly the average over the ensemble of random Hamiltonians and to calculate the complex eigenvalue distributions for the random non-Hermitian matrices, the localization length, Lyapunov exponents. Applications of the method to other quantum and classical systems with random Hamiltonians both discrete and continuous, are discussed. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z42.00004: First-Principles Study of Nuclear Quadruple Interaction of $^{19}$F* and Binding in Solid Fluorine D.R. Mishra, M.M. Aryal, N.P. Adhikari, S.R. Badu, R.H. Pink, R.H. Scheicher, Lee Chow, T.P. Das We have studied the binding energy (BE) and nuclear quadrupule interaction (NQI) parameters for the $^{19}$F* excited nuclear state in solid fluorine as part of our investigation [1] of the properties of solid halogens using the first principles Hartree-Fock Cluster procedure combined with many-body perturbation theory (MBPT), implemented by the Gaussian set of programs. Our results show that Van der Waals interaction obtained from intermolecular electron correlation effects has dominant influence on the BE but negligible effect on the NQI parameters. For the latter, ourcalculated e$^{2}$qQ is 119.0MHz using for Q(19F*), the value of 0.072 *10$^{-28}$m2 [2], and $\eta $, the asymmetry parameter, is essentially zero. The influence of rotational vibrational effects on e$^{2}$qQ is being investigated using a first-principles procedure [3] to bridge the small remaining difference with experiment (127.2 MHz) for e$^{2}$qQ [4]. [1] M.M. Aryal et al., Hyperfine Interact, 176, 51 (2007). [2] K.C.Mishra et al.,Phys. Rev.B25, 3389(1982). [3] N. Sahoo et al. Phys. Rev. Lett. 50, 913(1983) [4] H. Barfuss et al., Phys. Lett. 90A, 33(1982) [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z42.00005: Ab initio Calculations of X-ray Spectra: Comparison with Accurate Measurements J. J. Kas, J. J. Rehr, F. D. Vila A number of advances in the theory of x-ray absorption (XAS) have been developed with the aim of achieving a parameter-free treatment of the key many-body effects.\footnote{J. J. Rehr et al., Comptes Rendus Physique, {\bf 10}, 548 (2009)} These include a GW many-pole self-energy model, {\it ab initio} Debye-Waller factors, and an RPA screened core-hole. These developments have been implemented in the real-space multiple-scattering code FEFF9.0, and applied to calculations of x-ray absorption spectra and electron energy loss spectra as well as a variety of other core level spectroscopies. Calculations span a broad spectrum from the visible to x-ray energies. Results for a number of materials are compared with previous theories and with accurate experimental data. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z42.00006: Ab initio investigation of magnetic transport properties by Wannier interpolation Yugui Yao, Yi Liu An efficient ab initio approach for the study of magnetic transport properties is developed based on the Boltzmann equation with the Wannier interpolation scheme. Using this method, we can investigate magnetoresistance [1], low field Hall coefficient, anomalous Hall effect, orbit magnetization, cyclotron motion and the effective mass, etc. As a typical application of this method, we present the band-resolved electric conductivities of MgB$_{2}$ under finite magnetic fields, multiband characters for the individual bands are revealed. Combined with experimental result, fully band resolved scattering rate for each band was obtained for MgB$_{2}$. It seems that the scattering from el-ph coupling or impurities affects the $\pi _{1}$ band more weakly [2]. \\[4pt] [1] Yi Liu, Hai-Jun Zhang, and Yugui Yao, Phys. Rev. B 79, 245123 (2009); \\[0pt] [2] H. Yang, et al. Phys. Rev. Lett 101, 067001 (2008). [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z42.00007: Dynamical Mean-Field Theory approach to study the magnetic properties of nanostructures Neha Nayyar, Volodymyr Turkowski, Talat S. Rahman We extend the Nanoscale Dynamical Mean-Field Theory (NDMFT) approach [1] to study the magnetic properties of nanosystems. It is shown that the NDMFT solution becomes more accurate when the number of atoms in the cluster and their coordination number increase. We applied this method to study the magnetic properties of small cobalt clusters. The dependence of the cluster magnetization on the geometry, temperature and Coulomb repulsion energy was analyzed. We estimate the value of the Coulomb repulsion energy parameter, which is necessary to reproduce the experimental results in the case of different clusters. We compare our results with other approximations including GGA and GGA+U. In particular, we show that the last approximation in general overestimates the role of correlation effects. [1] S. Florens, Phys. Rev. Lett. 99, 046402 (2007) [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z42.00008: First-principles based calculation of phonon spectra and related properties in disordered alloys Subhradip Ghosh, Biswanath Dutta The study of lattice vibrations in the presence of substitutionally disordered alloys is one of the most fascinating areas of condensed matter physics. A huge array of.experimental data is available for over nearly half a century awaiting interpretation of the microscopic understanding of the various kinds of disorder that play a role in the lattice dynamical properties of these alloys. The theoretical calculations, on the other hand, were limited due to the lack of a suitable tool which can address both diagonal(mass) and off-diagonal(force-constant) disorder in these systems. This problem has been alleviated recently with the advent of the `Itinerant Coherent Potential Approximation'. In this work, we propose a first-principles based methodology to compute the phonon spectra and properties derivable from them. The method is a combination of first-principles density functional perturbation theory, the transferable force constant approach by Van De Walle et al (Rev. Mod. Phys. 74, 11(2002)) and Itinerant Coherent Potential Approximation. We present results for the phonon spectra and elastic constants of disordered FePd alloys. . [Preview Abstract] |
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