Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T23: Multiscale Modeling |
Hide Abstracts |
Sponsoring Units: DCOMP DMP Chair: Richard Lombardini, St. Mary's University Room: 202B |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T23.00001: Time Domain Propagation of Quantum and Classical Systems using a Wavelet Basis Set Method Richard Lombardini, Ewa Nowara, Bruce Johnson The use of an orthogonal wavelet basis set (Optimized Maximum-N Generalized Coiflets) to effectively model physical systems in the time domain, in particular the electromagnetic (EM) pulse and quantum mechanical (QM) wavefunction, is examined in this work. Although past research has demonstrated the benefits of wavelet basis sets to handle computationally expensive problems due to their multiresolution properties, the overlapping supports of neighboring wavelet basis functions poses problems when dealing with boundary conditions, especially with material interfaces in the EM case. Specifically, this talk addresses this issue using the idea of derivative matching creating fictitious grid points (T.A. Driscoll and B. Fornberg), but replaces the latter element with fictitious wavelet projections in conjunction with wavelet reconstruction filters. Two-dimensional (2D) systems are analyzed, EM pulse incident on silver cylinders and the QM electron wave packet circling the proton in a hydrogen atom system (reduced to 2D), and the new wavelet method is compared to the popular finite-difference time-domain technique. [Preview Abstract] |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T23.00002: A Hamiltonian theory of adaptive resolution simulations of classical and quantum models of nuclei Karsten Kreis, Davide Donadio, Kurt Kremer, Raffaello Potestio Quantum delocalization of atomic nuclei strongly affects the physical properties of low temperature systems, such as superfluid helium. However, also at room temperature nuclear quantum effects can play an important role for molecules composed by light atoms. An accurate modeling of these effects is possible making use of the Path Integral formulation of Quantum Mechanics. In simulations, this numerically expensive description can be restricted to a small region of space, while modeling the remaining atoms as classical particles. In this way the computational resources required can be significantly reduced. In the present talk we demonstrate the derivation of a Hamiltonian formulation for a bottom-up, theoretically solid coupling between a classical model and a Path Integral description of the same system. The coupling between the two models is established with the so-called Hamiltonian Adaptive Resolution Scheme, resulting in a fully adaptive setup in which molecules can freely diffuse across the classical and the Path Integral regions by smoothly switching their description on the fly. Finally, we show the validation of the approach by means of adaptive resolution simulations of low temperature parahydrogen. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T23.00003: Simulating long time behavior of materials: a case study of sintering of nanoparticles Amit Samanta, Selim Elhadj, Jeff Bude, Tammy Olson, Jon Lee, Jae Hyuck Yoo Physical processes in nature exhibit disparate time-scales, for example time scales associated with processes like phase transitions, various manifestations of creep, sintering of particles etc. are often much higher than time the system spends in the metastable states. The transition times associated with such events are also orders of magnitude higher than time-scales associated with vibration of atoms. Thus, atomistic simulations of such transition events is a challenging task. In this talk, I will present a method to overcome the time-scale problem and efficiently explore the free energy surface of a complex system. I will discuss how this method can be used to gain quantitative atomic-scale insights into the sintering of nanoparticles. The simulations suggest that processes like interfacial and bulk diffusion along with grain rotation play an important role during sintering. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-664253 [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T23.00004: Time-dependent potential-functional embedding theory Chen Huang, Florian Libisch, Qing Peng, Emily Carter We introduce a time-dependent potential-functional embedding theory (TD-PFET), in which atoms are grouped into subsystems. In TD-PFET, subsystems can be propagated by different suitable time-dependent quantum mechanical methods and their interactions can be treated in a seamless, first-principles manner. TD-PFET is formulated based on the time-dependent quantum mechanics variational principle. The action of the total quantum system is written as a functional of the time-dependent embedding potential, i.e., a potential-functional formulation. We derive the integral equation that such an embedding potential needs to satisfy. As proof-of-principle, we demonstrate TD-PFET for a Na4 cluster, in which each Na atom is treated as one subsystem and propagated by time-dependent Kohn-Sham density functional theory (TDDFT) using the adiabatic local density approximation (ALDA). Our results agree well with a direct TDDFT calculation on the whole Na4 cluster using ALDA. We envision that TD-PFET will ultimately be useful for studying ultrafast quantum dynamics in condensed matter, where key regions are solved by highly accurate time-dependent quantum mechanics methods, and unimportant regions are solved by faster, less accurate methods. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T23.00005: Coupled molecular-dynamics and first-principle transport calculations of metal/oxide/metal heterostructures Peter Zapol, Dmitry Karpeyev, Ketan Maheshwari, Xiaoliang Zhong, Badri Narayanan, Subramanian Sankaranarayanan, Michael Wilde, Olle Heinonen, Ivan Rungger The electronic conduction in Hf-oxide heterostructures for use in, e.g., resistive switching devices, depends sensitively on local oxygen stoichiometry and interactions at interfaces with metal electrodes. In order to model the electronic structure of different disordered configurations near interfaces, we have combined molecular dynamics (MD) simulations with first-principle based non-equilibrium Green's functions (NEGF) methods, including self-interaction corrections. We have developed an approach to generating automated workflows that combine MD and NEGF computations over many parameter values using the Swift parallel scripting language. A sequence of software tools transforms the result of one calculation into the input of the next allowing for a high-throughput concurrent parameter sweep. MD simulations generate systems with quenched disorder, which are then directly fed to NEGF and on to postprocessing. Different computations can be run on different computer platforms matching the computational load to the hardware resources. We will demonstrate results for metal-HfO2-metal heterostructures obtained using this workflow. [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T23.00006: Quasi-continuum multiscale theory for confined Lennard-Jones fluid mixture Mohammad H. Motevaselian, Sikandar Y. Mashayak, Narayana R. Aluru A continuum-based approach is developed to predict the structure of confined multicomponent Lennard-Jones fluids at multiple length-scales, ranging from few angstroms to microns. The continuum approach is based on the empirical potential-based quasi-continuum theory (EQT) that incorporates atomistic detail into a continuum framework such as the Nernst-Planck equation. It can also be used to construct a grand potential functional for classical density functional theories (cDFT). EQT and cDFT combination, provide a simple and fast approach to predict the inhomogeneous density, potential profiles and thermodynamic properties of confined fluids. In this work, we demonstrate EQT-cDFT approach by simulating a mixture of methane and hydrogen inside slit-like channels of graphene. We show that the structure of the confined mixture compares well with MD simulation results. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T23.00007: Multiscale Investigations of the Oxidation of Stepped Cu Surfaces Qing Zhu, Wissam Saidi, Judith Yang Defects on metal surfaces can induce non-canonical oxidation channels that may lead to the formation of novel nanostructures. Cu surfaces have been actively researched in the surface science community due to their wide range of applications in many fields. Recently, in situ TEM experiments showed that the oxidation of stepped surfaces promotes the formation of a flat metal-oxide interface through the Cu adatoms detachment from steps and diffusion across the terraces. In order to better understand these results, and to provide a tight bridge between the experiment and theory, we have investigated the Cu (100) oxidation using a multiscale computational approach that employs density functional theory and reactive force field. Our results demonstrate that the step-edge defects induce markedly different oxidation dynamical behavior compared to the flat surface. Additionally, on the stepped-surfaces, we find that the oxidation of the upper-terrace are more favored than the lower-terrace. We show that is behavior is due to a negative Ehrlich-Schwoebel diffusion barrier for oxygen in the ascending direction. The favoring of the oxidation of the top terrace drives Cu diffusion flux from the upper-terrace to the lower-terrace that explains the recent TEM experiments. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T23.00008: A systematically improvable second-principles method including electron and lattice degrees of freedom Pablo Garcia-Fernandez, Jacek Wojde\l, Jorge \'I\~niguez, Javier Junquera One of the most difficult tasks when trying to expand Density Functional Theory (DFT) calculations to large systems is the scaling of computational time with the number of electrons in the simulation box. However, not all electrons play a relevant role in the determination of the physical magnitude under scrutiny. In this work we present a systematic approximation to DFT based on a rigorous separation of these active electrons and holes from those of a reference state. Using a similar expansion to that found in Tight-binding DFT methods we obtain a large term containing the energy of the reference system, and a second, much smaller one, associated to the active part of the electron density. We associate the energy of the reference system to the lattice degrees of freedom and use a well-tested model Hamiltonian to represent them, on the other hand, the active electrons are described using a small but accurate Wannier function basis-set. Combined with an efficient Lanczos-based diagonalization, our method provides a systematically improvable scheme to simulate systems including tens of thousands of atoms under experimental conditions. We provide several examples of its application in the field of transition-metal oxides. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T23.00009: Mesoscale modeling of functional properties in core-shell nanoparticles John Mangeri, Olle Heinonen, Dmitry Karpeev, Serge Nakhmanson Core-shell nanoparticle systems of Zn-ZnO and ZnO-TiO$_2$ are studied computationally using the highly scalable MOOSE finite-element framework, developed at Idaho National Lab. The elastic anisotropic mismatch of the core and shell create an imprinting effect within the shell that produces a wide variation of strains. Due to this diversity of strains, the sharp band gap edges of the bulk semiconductor are observed to be ``thinned-out'' much like amorphous silicon. We show that a variety of factors, such as particle size, core-to-shell volume ratio, applied hydrostatic pressure, shell microstructure, as well as the effect of surface elasticity, can influence the distribution of optical band-gap values within the particle, which may prove useful within the field of photovoltaics. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T23.00010: The impact of resolution upon the complexity, information, thermodynamics, and transferability of coarse-grained models Thomas Foley, M. Scott Shell, William Noid By eliminating atomic degrees of freedom, coarse-grained (CG) models allow highly efficient simulations of complex phenomena. However, as a consequence of changing the model resolution, the coarse-graining procedure alters the apparent thermodynamic properties and model transferability. The present work analyzes the effects of model resolution upon the exact many-body potential of mean force (PMF), $W$, and, in particular, its entropic component, $S_W$. We demonstrate that $S_W$ quantifies the loss of information from the atomistic model and impacts the complexity, thermodynamics, and transferability of the CG model. In order to investigate these formal results, we analytically calculate the exact PMF for the popular Gaussian Network Model of proteins and quantify both the energy-entropy balance as well as the entropic contribution to intramolecular interactions as a function of resolution. Interestingly, seven diverse proteins demonstrate strikingly similar shifts in energy-entropy balance with decreasing model resolution. We expect that these results may provide general insight into both the thermodynamic properties and transferability of coarse-grained models for soft materials. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T23.00011: Calculation of energy relaxation rates of fast particles by phonons in crystals Micah Prange, Luke Campbell, Dangxin Wu, Sebastien Kerisit We present \textit{ab initio} calculations of the temperature-dependent exchange of energy between a classical charged point-particle and the phonons of a crystalline material. The phonons, which are computed using density functional perturbation theory (DFPT) methods, interact with the moving particle via the Coulomb interaction between the density induced in the material by phonon excitation and the charge of the classical particle. Energy relaxation rates are computed using time-dependent perturbation theory. The method, which is applicable wherever DFPT is, is illustrated with results for several important scintillators whose performance is affected by electron thermalization. We discuss the influence of the form assumed for quasiparticle dispersion on theoretical estimates of electron cooling rates. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T23.00012: Using the IRC n-Tiered model to generate exact numeric solutions for possible leptons Aran Stubbs Our model has 3 tiers below leptons and quarks: proto-matter, mezzo-matter, and infra-matter. Each has characteristic tachyons binding together the lower level structures to produce the higher level. Each class of tachyon generates its own granularity constant. The proto-matter is bound by gravitons to form the leptons and quarks. The mezzo-matter is bound by mezzo-tachyons to form the proto-matter. The infra-matter is bound by infra-tachyons to form the mezzo-matter. 2 types of mezzo tachyons bind the mezzo-matter structures: a charge tachyon binding s mezzo-matter (with $l$ $=$0), and a color tachyon binding structures with $l$\textgreater 0. The s structure has 1 infra-tachyon and 1 infra-photon, in 1s orbits. The p structure has 7 of each: among 4 s sub-shells and 1 p. The d structure has 11 s sub-shells, 3 p, and 1 d. Etc. Based on the first 2 leptons, a solution for the energy of the s (charge) structure, and the p (color) structure were deduced, from which the other mezzo structures energies were generated. From the mezzo matter energy content, and a pattern of orbits at the proto-matter level, energies for the next few leptons were found (to 3 sig figs): 140 MeV, 827 MeV, 1780 MeV, and 4690 MeV. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T23.00013: A variational free-energy functional approach to the Schr\"{o}dinger-Poisson theory Francisco J. Solis, Vikram Jadhao, Kaushik Mitra, Monica Olvera de la Cruz In the numerical simulation of model electronic device systems, where electrons are typically under confinement, a key obstacle is the need to iteratively solve the coupled Schr\"{o}dinger-Poisson equation in order to obtain the electronic potential. We show that it is possible to bypass this obstacle by adopting a variational approach and obtaining the solution of the SP equation by minimizing a functional. We construct the required functional and establish some of its properties. We apply this formulation to the case of narrow channel quantum wells where the local density approximation yields accurate results. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T23.00014: Ab initio quantum transport in atomic carbon chains Andr\'es R. Botello-M\'endez, Jean-Christophe Charlier, Florian Banhart Carbyne, the \textit{sp}-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. Recently, detailed electrical measurements and first-principles electronic transport calculations have been performed on monoatomic carbon chains [1]. When the 1D system is under strain, the current-voltage curves exhibit a semiconducting behavior, which corresponds to the polyyne structure of the atomic chain with alternating single and triple bonds. Conversely, when the chain is unstrained, the ohmic behavior is observed in agreement with the metallic cumulene structure with double bonds, confirming recent theoretical predictions, namely that a metal-insulator transition can be induced by adjusting the strain. The key role of the contacting leads is also scrutinized by \textit{ab initio} quantum conductance calculations [2], explaining the rectifying behavior measured in monoatomic carbon chains in a non-symmetric contact configuration.\\[4pt] [1] O. Cretu, A. R. Botello-Mendez, I. Janowska, C. Pham-Huu, J.-C. Charlier, and F. Banhart, Nano Lett. 13, 3487-3493 (2013).\\[0pt] [2] A. La Torre, A. R. Botello-Mendez, W. Baaziz, J.-C. Charlier, and F. Banhart, submitted for publication (2014). [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T23.00015: Development of a non-equilibrium quantum transport calculation method based on constrained density functional Han Seul Kim, Yong-Hoon Kim We report on the development of a novel first-principles method for the calculation of non-equilibrium quantum transport process. Within the scheme, non-equilibrium situation and quantum transport within the open-boundary condition are described by the region-dependent $\Delta $ self-consistent field method and matrix Green's function theory, respectively. We will discuss our solutions to the technical difficulties in describing bias-dependent electron transport at complicated nanointerfaces and present several application examples. [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. |
© 2020 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700