Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B20: Electronic Structure Methods I |
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Sponsoring Units: DCOMP Chair: Oliver Albertini, Georgetown University Room: 319 |
Monday, March 14, 2016 11:15AM - 11:27AM |
B20.00001: An Accurate Density Functional from Exchange-Correlation Hole Jianmin Tao, Yuxiang Mo The exchange-correlation hole is most fundamentally important in the development and understanding of density functional theory (DFT). However, due to the nonlocal nature of the exchange-correlation hole, development of DFT from the underlying hole presents a great challenge, and the works along this direction are limited. Here I will discuss a novel nonempirical DFT based on a semilocal hole, which is obtained from the density matrix expansion. Extensive tests on molecules and solids show that this functional can achieve remarkable accuracy for wide-ranging properties in condensed matter physics and quantum chemistry. [Preview Abstract] |
Monday, March 14, 2016 11:27AM - 11:39AM |
B20.00002: Assessment of a New Semilocal Density Functional on Molecules and Solids Yuxiang Mo, Jianmin Tao We have recently developed a new semilocal density functional based on the exchange hole (localized under a general coordinate transformation) from density matrix expansion, instead of imposing energy constraints to the functional or fitting it to a training set of properties. This functional is comprehensively evaluated on diverse properties of molecules and solids, including atomization energies for G2/97 (148 molecules), enthalpies of formation for G3-3 (75 molecules), ionization potentials for G3/99 (86 species), electron affinities for G3/99 (58 species), proton affinities (8 molecules), bond lengths for T-96R (96 molecules), vibrational frequencies for T-82F (82 molecules), 10 hydrogen bonded complexes, as well as lattice constants, bulk moduli, and cohesive energies for solids. Our tests show that the functional is remarkably accurate for these wide-ranging properties. [Preview Abstract] |
Monday, March 14, 2016 11:39AM - 11:51AM |
B20.00003: Benchmarking Post-SCF Treatments of Spin-Orbit Coupling in Electronic Structure Theory William Paul Huhn, Volker Blum Spin-orbit coupling (SOC) is an essential aspect of the electron band structures for all but the lightest-element materials. SOC is often incorporated into density-functional theory (DFT) calculations in a second-order variational approach, applying the SOC correction based on the orbitals from a scalar-relativistic self-consistent calculation. This talk compares the quality of non-self-consistent and self-consistent SOC corrections for a test set of over 100 different materials spanning the periodic table. We quantitatively compare entire DFT band structures from two benchmark-quality full-potential all-electron codes, i.e., the numeric atom-centered orbital code FHI-aims and the linearized augmented plane-wave code WIEN2k, based on the semilocal PBE functional. Few-meV agreement between non-self-consistent and self-consistent SOC is shown for elements up to row 4 of the periodic table, with agreement on the order of 10 meV for row 5 elements and differences exceeding 100 meV emerging for row 6 elements. We find little difference in SOC splittings between the PBE functional and the hybrid HSE06 functional. [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:03PM |
B20.00004: Dielectric-dependent Density Functionals for Accurate Electronic Structure Calculations of Molecules and Solids Jonathan Skone, Marco Govoni, Giulia Galli Dielectric-dependent hybrid [DDH] functionals [1] have recently been shown to yield highly accurate energy gaps and dielectric constants for a wide variety of solids, at a computational cost considerably less than standard GW calculations. The fraction of exact exchange included in the definition of DDH functionals depends (self-consistently) on the dielectric constant of the material. In the present talk we introduce a range-separated (RS) version of DDH functionals [2] where short and long-range components are matched using material dependent, non-empirical parameters. Comparing with state of the art GW [3] calculations and experiment, we show that such RS hybrids yield accurate electronic properties of both molecules and solids, including energy gaps, photoelectron spectra and absolute ionization potentials. [1] See, e.g. Skone et. al. PRB 89 195112 (2014) [2] Skone et. al. PRB (to be submitted) [3] Govoni and Galli JCTC 11 2680 (2015) [Preview Abstract] |
Monday, March 14, 2016 12:03PM - 12:15PM |
B20.00005: Quest for a semi-empirical MGGA functional with tight bound Bernard Delley A numerically robust parametrization for a meta-GGA exchange functional approximation has been obtained by optimization of bond energies in a database of 303 species.The variables, density, gradient and kinetic energy density, are useful to differentiate efficiently among the wide variety of bonding types in the database. The resulting MGGA rivals the thermochmistry accuracy of composite quantum chemistry approaches when applied to a wider data set of 592 species. Noticeable improvements over GGA's are also obtained for solid state properties. The present functional shows some similarities with the recently presented SCAN functional of Sun, Ruscinszky and Perdew. With the easily available semi-nonlocality through gradients and a kinetic energy density,this MGGA is widely widely applicable for molecular- as well as for extended systems and surface models. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B20.00006: Modeling Spin Fluctuations and Magnetic Excitations from Time-Dependent Density Functional Theory Tommaso Gorni, Iurii Timrov, Andrea Dal Corso, Stefano Baroni Harnessing spin fluctuations and magnetic excitations in materials is key in many fields of technology, spanning from memory devices to information transfer and processing, to name but a few. A proper understanding of the interplay between collective and single-particle spin excitations is still lacking, and it is expected that first-principle simulations based on TDDFT may shed light on this interplay, as well as on the role of important effects such as relativistic ones and related magnetic anisotropies. All the numerical approaches proposed so far to tackle this problem are based on the computationally demanding solution of the Sternheimer equations for the response orbitals or the even more demanding solution of coupled Dyson equations for the spin and charge susceptibilities. The Liouville-Lanczos approach to TDDFT has already proven to be a valuable alternative, the most striking of its features being the avoidance of sums over unoccupied single-particle states and the frequency-independence of the main numerical bottleneck. In this work we present an extension of this methodology to magnetic systems and its implementation in the \textsc{Quantum ESPRESSO} distribution, together with a few preliminary results on the magnon dispersions in bulk Fe. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B20.00007: Symmetry-adapted Wannier Functions from $L_1$ regularized Sparse Optimization Jiatong Chen, Ke Yin, Yi Xia, Vidvuds Ozolins, Stanley Osher, Russel Caflisch Wannier functions are widely used as real space representation of periodic solids in electronic structure calculation. We present a new approach to calculate symmetry-adapted Wannier functions which are directly obtained from variational principle of total energy plus an L1 regularization term, $\frac{1}{\mu} \int | \psi| d{\bf r}$. The obtained “compressed” Wannier functions are only nonzero within a finite region. With the help of induced group representation theory, we only need to calculate Bloch functions (in Wannier gauge) within irreducible Brillouin zone, while point group symmetry is strictly enforced. Implementation in plane waves-pseudopotential codes and application to real material system will be demonstrated. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B20.00008: Free energy from stationary implementation of the DFT+EDMFT functional Turan Birol, Kristjan Haule The workhorse of first principles calculations on crystalline solids is the Density Functional Theory at the level of Local Density Approximation (LDA). Despite its various successes, LDA is prone to an overbinding problem, which introduces an error in optimized lattice constants and other structural parameters. Various Generalized Gradient Approximations are introduced to correct for this problem, but they often fail to systematically correct it, in particular in correlated electron materials. We developed a stationary and functional derivable Embedded Dynamical Mean Field Theory combined with the DFT (EDMFT+DFT) to calculate the free energy and to optimize the structural parameters in correlated electron compounds. In our stationary formalism, the first order error in the density leads to a much smaller, second order error in the free energy. We consider the correlated metal SrVO$_3$, Mott insulating FeO, elemental Ce, and iron chalcogenide FeSe as examples to show that EDMFT predicts the lattice constants with high accuracy. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B20.00009: Relativistic Green's Functions in Full-Potential Multiple-Scattering Theory Xianglin Liu, Yang Wang, Markus Eisenbach, G.Malcolm Stocks The Green’s functions play a central role in MST based KKR method. Obtaining the Green’s functions by solving the Dirac equation is appealing since it naturally incorporated the electron spin and the spin-orbit coupling effects. Here we implemented the full-potential relativistic KKR method using a technique called the sine and cosine matrices formalism. The charge density and the density of states of some pure element crystals have been calculated. Different expressions of the Green’s functions have been investigated for numerical benefits. [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B20.00010: Understanding the Relativistic Generalization of Density Functional Theory (DFT) and Completing it in Practice. Diola Bagayoko In 2014, 50 years following the introduction of density functional theory (DFT), a rigorous understanding of it was published [AIP Advances, 4, 127104 (2014)]. This understanding included necessary steps ab initio electronic structure calculations have to take if their results are to possess the full physical content of DFT. These steps guarantee the fulfillment of conditions of validity of DFT; not surprisingly, they have led to accurate descriptions of several dozens of semiconductors, from first principle, without invoking derivative discontinuity or self-interaction correction. This presentation shows the mathematically and physically rigorous understanding of the relativistic extension of DFT by Rajagopal and Callaway \textbraceleft Phys. Rev. B 7, 1912 (1973)]. As in the non-relativistic case, the attainment of the absolute minima of the occupied energies is a necessary condition for the corresponding current density to be that of the ground state of the system and for computational results to agree with corresponding, experimental ones. Acknowledgments\textbf{: }This work was funded in part by the US National Science Foundation [NSF, Award Nos. EPS-1003897, NSF (2010-2015)-RII-SUBR, and HRD-1002541], the US Department of Energy, National Nuclear Security Administration (NNSA, Award No. DE-NA0002630), LaSPACE, and LONI-SUBR. [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B20.00011: Enhancing inter-tube conductivity in carbon nanotube networks Arash Mostofi, Robert Bell, Mike Payne Retaining the remarkable electronic transport properties of individual carbon nanotubes (CNTs) when scaling up to macroscopic CNT networks for use in devices remains a significant challenge. As no single tube spans the device, electrons must travel between CNTs to contribute to the conductivity. Conductivity between CNTs of different chirality is suppressed due to the requirement of momentum conservation. Using a combination of analytic theory and tight-binding, I will show that this limitation can be overcome by supplying a weak perturbation to the system, resulting in order of magnitude increases of conductivity\footnote{Phys. Rev. B 89, 245426 (2014)}. I will present practical realizations of such perturbations, which I will demonstrate using Landauer-Buttiker transport simulations based on large-scale density-functional theory calculations\footnote{Comput. Phys. Commun. 193, 78 (2015); www.onetep.org}. [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B20.00012: Data compression algorithms for electronic wave functions William Dawson, Francois Gygi Large scale, First-Principles Molecular Dynamics (FMPD) simulations require an large amount of computational effort. Unfortunately, the size of the data they generate and the overhead cost of saving it result in the overwhelming majority of this potentially valuable data being lost. The rising gap between CPU and file I/O performance will restrict even further the amount of data saved during future FPMD simulations. The Recursive Subspace Bisection method for generating localized wavefunctions has recently been utilized to reduce the cost of computing Hartree-Fock exchange with controlled accuracy. We show that a variation of this method can be used to compress FPMD simulation data. Furthermore, we show that this method has controlled and predictable accuracy, and can be applied without concern for specific system properties. We demonstrate this method by compressing data from the simulation of liquid water, melting silicon, and other representative systems. Supported by: DE-SC0008938. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B20.00013: Nonorthogonal generalized hybrid Wannier functions for large-scale DFT simulations Andrea Greco, John W. Freeland, Arash A. Mostofi Semiconductor-based thin-films have applications in microelectronics,from transistors to nanocapacitors. Many properties of such devices strongly depend on the details of the interface between a metallic electrode and the thin-film semiconductor/insulator. Hybrid Wannier Functions (WFs), extended in the surface plane, but localized along the direction normal to the surface/interface, have been successfully used to explore the properties of such heterostructures layered along a given direction, and are a natural way to study systems that are at the same time a 2D conductor (in plane) and a 1D insulator (out of plane). Current state-of-the art implementations of Hybrid WFs rely on first performing a traditional cubic-scaling density-functional theory (DFT) calculation. This unfavourable scaling precludes the applicability of this method to the large length scales typically associated with processes in realistic structures. To overcome this limitation we extend the concept of Hybrid WFs to nonorthogonal orbitals that are directly optimized in situ in the electronic structure calculation. We implement this method in the ONETEP large-scale DFT code and we apply it to realistic heterostructure systems, showing it is able to provide plane-wave accuracy but at reduced computational cost. [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B20.00014: Electronic correlation in magnetic contributions to structural energies Roger Haydock For interacting electrons the density of transitions [see http://arxiv.org/abs/1405.2288] replaces the density of states in calculations of structural energies. Extending previous work on paramagnetic metals, this approach is applied to correlation effects on the structural stability of magnetic transition metals. [Preview Abstract] |
Monday, March 14, 2016 2:03PM - 2:15PM |
B20.00015: Effective on-site Coulomb interaction and electron configurations in transition-metal complexes from constraint density functional theory Kenji Nawa, Kohji Nakamura, Toru Akiyama, Tomonori Ito, Michael Weinert Effective on-site Coulomb interactions ($U_{\mathrm{eff}})$ and electron configurations in the localized $d$ and $f$ orbitals of metal complexes in transition-metal oxides and organometallic molecules, play a key role in the first-principles search for the true ground-state. However, wide ranges of values in the $U_{\mathrm{eff}}$ parameter of a material, even in the same ionic state, are often reported. Here, we revisit this issue from constraint density functional theory (DFT) by using the full-potential linearized augmented plane wave method. The $U_{\mathrm{eff}}$ parameters for prototypical transition-metal oxides, TMO (TM$=$Mn, Fe, Co, Ni), were calculated by the second derivative of the total energy functional with respect to the $d$ occupation numbers inside the muffin-tin (MT) spheres as a function of the sphere radius. We find that the calculated $U_{\mathrm{eff}}$ values depend significantly on the MT radius, with a variation of more than 3 eV when the MT radius changes from 2.0 to 2.7 a.u., but importantly an identical valence band structure can be produced in all the cases, with an approximate scaling of $U_{\mathrm{eff}}$. This indicates that a simple transferability of the $U_{\mathrm{eff}}$ value among different calculation methods is not allowed. We further extend the constraint DFT to treat various electron configurations of the localized $d$-orbitals in organometallic molecules, TMCp$_{\mathrm{2}}$ (TM$=$Cr, Mn, Fe, Co, Ni), and find that the calculated $U_{\mathrm{eff}}$ values can reproduce the experimentally determined ground-state electron configurations. [Preview Abstract] |
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