Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y7: Quantum Monte Carlo and General Computational Physics |
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Sponsoring Units: DCOMP Chair: Michael Swift, University of California, Santa Barbara Room: 266 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y7.00001: Computations of fermion pairing by stochastic sampling in Hartree-Fock-Bogoliubov space Hao Shi, Shiwei Zhang We describe the computational ingredients for an approach to treat interacting fermion systems in the presence of pairing fields, based on path-integrals in the space of Hartree-Fock-Bogoliubov (HFB) wave functions\footnote{H.~\ Shi and S.~\ Zhang, ArXiv:1611.02689(2016). }. The path-integrals can be evaluated by Monte Carlo, via random walks of HFB wave functions whose orbitals evolve stochastically. The approach combines the advantage of HFB theory in paired fermion systems and many-body quantum Monte Carlo (QMC) techniques. A constrained-path or phaseless approximation can be applied to the random walks of the HFB states if a sign problem or phase problem is present. With these techniques, we study the nature of the superconducting order in the two-dimensional Hubbard model by applying an external pairing finning field. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y7.00002: Interaction-driven ground states in strained graphene from functional renormalization Michael Scherer, David Sanchez de la Pena, Julian Lichtenstein, Carsten Honerkamp We study the interaction-driven instabilities of electrons on the half-filled honeycomb lattice as a model for graphene employing realistic tight-binding and Coulomb interaction parameters. To this end, we employ an implementation of functional renormalization group equations allowing for a high-definition resolution of the interaction vertex' wavevector dependence. We connect to previous lattice quantum Monte Carlo (QMC) results which predict a stabilization of the semimetallic phase for ab initio interaction parameters and confirm that the application of a finite biaxial strain can induce a quantum phase transition towards an ordered ground state. In contrast to QMC simulations which have to avoid the occurrence of a sign problem, our approach is not limited in the choice of tight-binding and interaction parameters. Here, we investigate a range of parameters which are not accessible by QMC, e.g., by take into account an extended tight-binding Hamiltonian for a more accurate description of the band structure of graphene's $p_z$ electrons. Besides the antiferromagnetic ground state, we find other instabilities to become leading, e.g. an incommensurate charge density wave phase and a novel extended $s$-wave pairing state. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y7.00003: Computations of Surface Energy by Diffusion Quantum Monte Carlo Method Cheng-Rong Hsing, Ching-Ming Wei One of the most important quantities in studying a surface is the surface energy, but the direct experimental measurement is difficult. Therefore theoretical modelling is very important. Nowadays, density functional theory (DFT) is the most commonly used electronic structure method for studying material properties; however, the accuracy of DFT results often depends on the choice of exchange-correlation (XC) functional. By using a more accurate method for treating XC effects, the diffusion quantum Monte Carlo (DMC) method [Rev. Mod. Phys. 73, 33 (2001)] has been applied to study MgO and LiH surfaces [ J. Phys.: Condens. Matter 18, L435–L440 (2006); Phys. Rev. B 82, 165431 (2010)]. The DMC results reveal that the local density approximation (LDA) predicts a better value than the generalized gradient approximation (GGA). In this work, we present the results of the surface energy for various surfaces (NaCl, LiH, MgO, TiO2, C, Si, Be, Mg, Al and Al2O3) using DMC and DFT with LDA, PBE and PBEsol functionals. Taking DMC surface energies as the benchmark, LDA, PBE and PBEsol functionals underestimate the surface energy, except for LiH, Be, Mg and Al2O3 surfaces where LDA and PBEsol predict the similar values as DMC calculation. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y7.00004: Monte Carlo calculation of bound states in quantum mechanics: regular potentials Maria Anabel Trejo, James P Edwards, Urs Gerber, Christian Schubert, Axel Weber The calculation of bound state energies by a direct or variational Monte Carlo evaluation of the quantum mechanical path integral has a long history. Here, we present a new approach that is an adaption of techniques originally developed in quantum field theory. It allows us to obtain ground state energies from the large - time limit of the propagator for a large class of potentials. After discussing various algorithms for the generation of time-discretized paths, we present benchmark results for two non-singular potentials for which the propagator is known in closed form, the harmonic oscillator and the symmetric P\"{o}schl-Teller potential. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y7.00005: Modeling Particle Motion Through Electret Filter Media Dana Rottach Filtering facepiece respirators (FFR) stockpiled for use during public health emergencies such as an infectious disease outbreak or pandemic can be subjected to conditions which could lead to performance degradation. The traditional picture of small particle capture by fibrous filter media qualitatively separates the effect of inertial impaction, interception from the streamline, diffusion, settling, and electrostatic attraction. Most of these mechanisms depend upon stable conformational properties. However, common FFR rely on electrets to achieve their high performance, and over time heat and humidity can cause degradation. A single-particle Newtonian dynamics simulation including a stochastic diffusive term, a hydrodynamic Stokes term, and a term representing an electret-induced dipole attraction has been developed to allow simultaneous consideration of the traditionally separated filtration modes. The electret term is allowed to decay between successive runs to mimic aging of the media. The initial simulations simulate particle collection by a single fiber using the 2D Kuwabara expression for fluid flow around a fiber. Subsequent simulations will use more realistic 3D fiber configurations with the fluid flows precalculated using traditional computational fluid dynamics. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y7.00006: Anisotropic frictional heat dissipation in cyclotrimethylene trinitramine Pankaj Rajak, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Anisotropic frictional response and corresponding heat dissipation from different crystallographic planes of RDX crystal is studied using molecular dynamics simulations. The effect of frictional force on the nature of damage and system temperature is monitored along different directions on primary slip plane, (010), of RDX and on non-slip planes, (100) and (001). The correlation between the friction coefficient, deformation and the frictional heating in these system is determined. It is observed that friction coefficients on slip planes are smaller than those of non-slip planes. In response to friction on slip plane, RDX crystal deforms via dislocation formation and shows less heating. On non-slip planes due to the inability of the system to deform by dislocation formation, large temperature rise is observed in the system just below the contact area of two surfaces. Frictional sliding on non-slip planes also lead to the formation of damage zone just below the contact area of two surfaces due to the change in RDX ring conformation from chair to boat/half-boat. [Preview Abstract] |
(Author Not Attending)
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Y7.00007: Abstract Withdrawn
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Friday, March 17, 2017 12:39PM - 12:51PM |
Y7.00008: Transport in flat band lattice models with Hermitian and non-Hermitian perturbations Hee Chul Park, Jung-Wan Ryu, Nojoon Myoung We study the effect of Hermitian and non-Hermitian perturbations in flat band lattice models. In the flat band lattice models with non-Hermitian perturbations, we show that non-Hermitian degenerate points, so-called exceptional points, can appear in complex band structures. We also report additional dip and gap structures in transmissions, which cannot be appeared in band structures in cases of Hermitian and non-Hermitian perturbations, respectively. We investigate the Fano resonance and the unexpected band structure in a single particle transport on flat band lattice models. The imperfection of channel opening makes the particle to destructively interfere between transmitted and localized states due to the broken symmetry. In case of the non-Hermitian systems in which complex band structures can appear, PT symmetry gives rise to special degenerate points, so-called exceptional points, and the band gap emerges nearby flat band from this symmetric system satisfying energy balances. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y7.00009: NEW ADVANCEMENTS IN THE STUDY OF THE UNIFORM ELECTRON GAS WITH FULL CONFIGURATION INTERACTION QUANTUM MONTE CARLO Michele Ruggeri, Hongjun Luo, Ali Alavi Full Configuration Interaction Quantum Monte Carlo (FCIQMC) [1] is able to give remarkably accurate results in the study of atoms and molecules. The study of the uniform electron gas (UEG) on the other hand has proven to be much harder, particularly in the low density regime. The source of this difficulty comes from the strong interparticle correlations that arise at low density, and essentially forbid the study of the electron gas in proximity of Wigner crystallization. We extend a previous study on the three dimensional electron gas [2] computing the energy of a fully polarized gas for N=27 electrons at high and medium density ($r_{S} = 0.5$ to $5.0$). We show that even when dealing with a polarized UEG the computational cost of the study of systems with $r_{S}>5.0$ is prohibitive; in order to deal with correlations and to extend the density range that to be studied we introduce a basis of localized states and an effective transcorrelated Hamiltonian.\newline \quad\newline [1] G. H. Booth, A. J. W. Thom and A. Alavi, J. Chem. Phys. {\bf 131} 054106 (2009)\newline [2] J. J. Shepherd, George H. Booth and A. Alavi, J. Chem. Phys. {\bf 136} 244101 (2012) [Preview Abstract] |
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