Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T13: Electronic Structure |
Hide Abstracts |
Sponsoring Units: DCOMP Chair: David Vanderbilt, Rutgers University Room: 309 |
Wednesday, March 18, 2009 2:30PM - 2:42PM |
T13.00001: Three-dimensional statistical reduction of the non-relativstic Schr\"{o}dinger equation for electrons with pair-wise Coulomb interactions Boyan Obreshkov Based on Ritz variational principle, we reduce in statistical fashion the non-relativistic $N$-body Schr\"{o}dinger equation for electrons with Coulomb interactions to a three-dimensional wave-equation for the motion of one electron with the residual $N-1$ electrons acting spectators of its motion [1]. As a consequence the Pauli's exclusion principle is interpreted as dynamical principle. Analytic solutions of the all electron quantal equations for the ground and excited states of the helium and lithium isoelectronic sequences will be represented and the comparison with the experimental measurements for the ground-state ionization potentials of atoms shown. \\[0pt] [1] B.~D.~Obreshkov , Phys.~Rev.~A {\bf 78}, 032503 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 2:42PM - 2:54PM |
T13.00002: High Pressure Phases of Cu2O David Groh, Ravi Pandey, Miguel Blanco Copper Oxide's ambient phase is cubic. The copper atoms are in a simple face centered cubic packing sequence of hexagonal layers, with the oxygen atoms at alternating tetrahedral sites. As the pressure increases, cubic symmetry breaks. While the basic packing sequence is maintained, the distance between layers is no longer cubic -- a hexagonal structure results. At even further pressures, a major crystal structure change occurs to the CdI2 structure. The calculated phase change pressures and volumes tend to compare well with experiment. [Preview Abstract] |
Wednesday, March 18, 2009 2:54PM - 3:06PM |
T13.00003: $\bf{k}\cdot\bf{p}$ formalism within FLAPW method Tatsuya Shishidou, Tamio Oguchi We provide $\bf{k}\cdot\bf{p}$ formalism within the full-potential linearized augmented plane wave (FLAPW) method. Unlike the pure plane waves, the LAPW functions do not behave trivially in moving from $\bf{k}$ to $\bf{k}+\bf{q}$ and their incompleteness as a basis set should be taken into account. Derivatives of the sphere matching coefficients play the key role, for which we find a simple formula. Concrete formula for the $\bf{k}\cdot\bf{p}$ matrix elements is derived and numerically tested. Generalized second-order perturbation theory allowing for a degenerate case is presented and the literally-exact electronic band gradients and curvatures are accessible. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T13.00004: Electric polarization in a Chern insulator Sinisa Coh, David Vanderbilt We extend the Berry-phase concept of polarization to insulators having a non-zero value of the Chern invariant. The generalization to such Chern insulators requires special care because of the partial occupation of chiral edge states. We show how the integrated bulk current arising from an adiabatic evolution can be related to a difference of bulk polarizations. We also show how the surface charge can be related to the bulk polarization, but only with a knowledge of the wavevector at which the occupancy of the edge state is discontinuous. We conclude by presenting numerical calculations on a model Hamiltonian to provide additional support for our analytic arguments.\footnote{Preprint: arXiv:0810.4549} [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T13.00005: A new Laplacian representation for real-space calculations of general periodic and partially periodic systems Amir Natan, Ayelet Benjamini, Doron Naveh, Leeor Kronik, Murilo Tiago, Scott Beckman, James Chelikowsky We present a real-space method for electronic-structure calculations of systems with general full or partial periodicity. The method is based on the self-consistent solution of the Kohn-Sham equations, using first principles pseudopotentials, on a uniform three-dimensional non-Cartesian grid. Its efficacy derives from the introduction of a new generalized high-order finite-difference Laplacian that avoids the numerical evaluation of mixed derivative terms and results in a simple yet accurate finite difference operator. Our method is further extended to systems where periodicity is enforced only along some directions (e.g., surfaces), by setting up the correct electrostatic boundary conditions and by properly accounting for the ion-electron and ion-ion interactions. Our method enjoys the main advantages of real-space grid techniques over traditional plane-wave representations for density functional calculations, namely, improved scaling and easier implementation on parallel computers, as well as inherent immunity to spurious interactions brought about by artificial periodicity. We demonstrate its capabilities on bulk GaAs and Na for the fully periodic case and for a monolayer of Si-adsorbed polar nitrobenzene molecules for the partially periodic case. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T13.00006: Confinement effects on excitation energies and regioselectivity as probed by the Fukui function and the molecular electrostatic potential Alex Borgoo, David Tozer, Paul Geerlings, Frank De Proft When a molecule is placed as a guest inside a zeolite pore, its electronic structure will be altered, among others by the effect of the so-called ``confinement". It has been established that the compression of the molecular orbitals influences a system's reactivity. In this work we use a simple potential barrier method to quantify the importance of confinement effects on chemical reactivity. In the first part, excitation energies and molecular orbital energy gaps are evaluated for molecules placed in cavities of different sizes. Our results for ethylene and formaldehyde reveal an increase in excitation energy and the gap between the occupied and the unoccupied levels. In the case of the larger molecules naphthalene and anthracene, the HOMO-LUMO gap shows very little sensitivity to the confinement. To investigate the role of confinement effects on local aspects of chemical reactivity and on regioselectivity, we evaluated its effect on the Fukui function and the molecular electrostatic potential, reactivity indices that are central in the description of orbital and charge controlled reactions. The results indicate that confinement can influence the regioselectivity and that the reactivity of anions is expected to change, due to the artificial binding of the exess electron. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T13.00007: Maximally-localized Wannier functions for GW quasiparticles D. R. Hamann, David Vanderbilt Recent efforts carrying the GW many-body approximation to self-consistency have given improved electronic structure results.$^{1}$ Maximally-localized Wannier functions$^{2}$ formed from the quasiparticle wave functions$^{3}$ provide an efficient and highly accurate basis for interpolating the SCGW bands from a coarse Brillouin-zone mesh to symmetry lines. Since the MLWF's correspond to chemists' bond orbitals, they potentially also provide insight into the qualitative effects of the improved treatment of correlations in SCGW compared to LDA. We report results on SrTiO$_{3}$, solid Ar, and molecular CO. Band interpolation is accurate and effective for both solids. Small shifts in the degree of hybridization can be visualized for some of the SrTiO$_{3}$ and CO MLWF's. In Ar, individual conduction-band Bloch functions were found to have large differences between LDA and SCGW.$^{1}$ However, a manifold of 9 d and spd-hybrid MLWF's which proved to be the minimum necessary for the lower conduction bands showed minimal differences in the two cases. A fully-functional interface to the \textsc{WANNIER90} library within the SCGW-capable \textsc{ABINIT} code has been implemented and will be publicly available in the near future. 1. F. Bruneval \textit{et al}., Phys. Rev. B \textbf{74}, 045102 (2006). 2. N. Marzari and D. Vanderbilt, Phys. Rev. B \textbf{56}, 12 847 (1997). 3. M. van Schilfgaarde \textit{et al}., Phys. Rev. Lett. \textbf{96}, 226402 (2006). [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T13.00008: High-performance computational condensed-matter physics in the cloud J.J. Rehr, L. Svec, J. P. Gardner, M. P. Prange We demonstrate the feasibility of high performance scientific computation in condensed-matter physics using {\it cloud computers} as an alternative to traditional computational tools. The availability of these large, virtualized pools of compute resources raises the possibility of a new compute paradigm for scientific research with many advantages. For research groups, cloud computing provides convenient access to reliable, high performance clusters and storage, without the need to purchase and maintain sophisticated hardware. For developers, virtualization allows scientific codes to be pre-installed on machine images, facilitating control over the computational environment. Detailed tests are presented for the parallelized versions of the electronic structure code SIESTA \footnote{J. Soler et al., J. Phys.: Condens. Matter {\bf 14}, 2745 (2002).} and for the x-ray spectroscopy code FEFF \footnote{A. Ankudinov et al., Phys. Rev. B {\bf 65}, 104107 (2002).} including CPU, network, and I/O performance, using the the Amazon EC2 Elastic Cloud. [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T13.00009: A scalable algorithm for the computation of Hartree-Fock exchange Ivan Duchemin, Francois Gygi Electronic structure calculations based on hybrid density functionals require efficient algorithms for the computation of the Hartree-Fock exchange operator. The high computational cost of Hartree-Fock exchange currently limits the use of such functionals in large-scale First-Principles Molecular Dynamics applications. We present a scalable parallel algorithm for the computation of Hartree-Fock exchange in a plane-wave, pseudopotential framework, with applications to electronic structure calculations of liquid water and various nanostructures. Technical issues arising in the implementation of hybrid density functionals will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T13.00010: Compact representations of Kohn-Sham invariant subspaces Francois Gygi We present a method to compute a hierarchical approximate representation of the solutions of the Kohn-Sham equations. The approach is based on a recursive bisection algorithm and yields one-particle wavefunctions localized on domains of varying sizes. The accuracy of the representation is set {\em a priori} by specifying the maximum error in the norm of the approximate wavefunctions. Applications to the electronic structure of large systems are used to illustrate the data reduction achieved by this representation. The achievable data compression is similar to that obtained by truncating Maximally Localized Wannier Functions. Implications for the acceleration of electronic structure calculations and for the development of linear-scaling algorithms will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 4:30PM - 4:42PM |
T13.00011: Improvements to the NRL Tight-Binding Model Michael Mehl, Dimitrios Papaconstantopoulos, Noam Bernstein, Daniel Finkenstadt, Stefano Curtarolo The original NRL Tight-Binding Method[1] has proven to be extremely successful in reproducing first-principles total energies and band structures for many elemental systems[2], and has been applied in computationally intensive molecular dynamics simulations[3]. When generalizing to multiple atom types, however, some difficulties arise because of the form of the interaction of the on-site matrix elements with the external environment. We discuss these difficulties, and describe a new version of the method which includes a proper two-center development of the on-site parameters[4,5], including applications of the method. [1] RE Cohen et al., Phys. Rev. B 50, 14694 (1994) [2] MJ Mehl and DA Papaconstantopoulos, Phys. Rev. B 54, 4519 (1996) [3] D Finkenstadt et al., Phys. Rev. B 74, 184118 (2006) [4] JL Mercer and MY Chou, Phys. Rev. B 49, 8506 (1994) [5] RE Cohen et al., Phys. Rev. B 56, 8575 (1997) [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T13.00012: 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 coupling since its discovery only three 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, here 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] |
Wednesday, March 18, 2009 4:54PM - 5:06PM |
T13.00013: Entanglement Spectrum of Topological Insulators F. D. M. Haldane Topological order in electronic systems leads to striking features in the ``entanglement spectrum'' which characterizes quantum entanglement between two halves of a system (FDMH, PRL 101,101504 (2008)). If the system is divided along a translationally-invariant boundary, the spectrum can be labeled by momentum parallel to it, and is gapless if topological order is present. The gapless spectrum is related to gapless edge states that appear at free edges of such systems. Topological insulators have non-trivial one-electron band structure properties; the entanglement spectrum of a non-interacting electron Slater determinant state is itself a non-interacting fermionic spectrum. This spectrum is gapped for ``trivial'' ordinary insulating band structures, but exhbits characteristic spectral flow and gapless modes when the band structure is topologically non-trivial. As a case study, the entanglement spectrum of the ``Haldane model'' of a Bloch electron band structure with a zero-field quantum Hall effect will be described in detail, and generalizations to spin-orbit-coupled topological insulators discussed. [Preview Abstract] |
Wednesday, March 18, 2009 5:06PM - 5:18PM |
T13.00014: Trends in electron correlation effects on $^{17}$O NMR chemical shifts in the alkaline earth oxides. Eric J. Walter, Daniel L. Pechkis, Henry Krakauer A recent study found that calculated GGA chemical shift $\delta_{iso}$(O) in CaO and other Ca oxides were in poor agreement with experiment. We have calculated $\delta_{iso}$(O) in the rock salt series MgO through BaO, using a range of methods from HF and DFT to highly accurate CCSD calculations. The crystal environments were modeled with finite quantum clusters. GGA results for 25-atom O$_{19}$X$_6$ embedded clusters are found to i) reproduce previous GGA results with periodic boundary conditions for Mg and Ca\footnote{Profeta et al.\ J. Am. Chem. Soc. {\bf 126}, 12628 (2004).}; ii) yield poor results for SrO as in CaO; iii) give good agreement with experiment for BaO. 7-atom OX$_6$ clusters were used to study trends with increasing levels of correlation. For MgO, correlated treatments result in only small changes compared to HF and DFT, as expected. Both CaO and SrO show large changes due to improved treatment of correlation, with the GGA-CCSD $\delta_{iso}$(O) difference similar to the GGA-Expt difference in the larger clusters. CCSD OX$_6$ results for BaO were inconclusive, from competing errors due to relativistic and correlation effects. We discuss our results in terms of the increasing covalency in XO crystals with heavier cations. [Preview Abstract] |
Wednesday, March 18, 2009 5:18PM - 5:30PM |
T13.00015: Efficient all-electron $GW$ calculations of complex semiconductors Christoph Friedrich, Arno Schindlmayr, Stefan Bl\"ugel The $GW$ approximation for the electronic self-energy yields quasiparticle band structures in very good agreement with experiment, but almost all implementations so far are based on the pseudopotential approach, which limits their range of applicability. We have developed an implementation (SPEX, http://www.flapw.de/spex/) within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method. Within this method a large variety of materials can be treated, including d- and f-electron systems, oxides and magnetic systems. Our implementation employs a mixed product basis for the representation of wave-function products. A basis transformation to the eigenfunctions of the Coulomb potential allows a reduction of the basis-set size without compromising the accuracy, thus leading to a considerable speed-up in computation time. To demonstrate the efficiency of the implementation we present results for complex semiconductors. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700