Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S02: Developments of DFT: from Quantum to Statistical Mechanics (VI)Focus
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Sponsoring Units: DCP DCOMP GSNP Chair: Neepa Maitra, Hunter Coll Room: LACC 150B |
Thursday, March 8, 2018 11:15AM - 11:51AM |
S02.00001: Non-adiabatic dynamics on a single time-dependent potential energy surface Invited Speaker: Eberhard K Gross Some of the most fascinating quantum phenomena, such as the process of vision or phonon-driven superconductivity are examples of non-adiabatic dynamics where more than one Born-Oppenheimer surface is involved. To tackle such situations one has to face the full Hamiltonian of the complete system of electrons and nuclei. We deduce an exact factorization [Abedi, Maitra, Gross, PRL 105, 123002 (2010)] of the full electron-nuclear wavefunction into a purely nuclear part and a many-electron wavefunction which parametrically depends on the nuclear configuration and carries the meaning of a conditional probability amplitude. The equations of motion for these wavefunctions uniquely define the exact potential energy surface and the exact geometric phase, both in the time-dependent and in the stationary regime. We discuss a case where the exact Berry phase vanishes although there is a non-trivial Berry phase for the same system in Born-Oppenheimer approximation, implying that in this particular case the Born-Oppenheimer Berry phase is an artifact [Min, Abedi, Kim, Gross, PRL 113, 263004 (2014)]. In the time-domain, whenever there is a splitting of the nuclear wavepacket in the vicinity of an avoided crossing, the exact time-dependent surface shows a nearly discontinuous, moving step [Abedi, Agostini, Suzuki, Gross, PRL 110, 263001 (2013)] between adiabatic surfaces, reminiscent of Tully surface hopping. Based on this observation, we propose novel mixed-quantum-classical algorithms which provide a much improved (over surface hopping) description of decoherence [Min, Agostini, Gross, PRL 115, 073001 (2015)]. This is demonstrated for the laser-induced ring opening of the oxirane molecule [Min, Agostini, Tavernelli, Gross, JPCL 8, 3048 (2017)]. We present a multi-component density functional theory based on the exact factorization that provides an avenue to make the fully coupled electron-nuclear system tractable also for large systems [Requist, Gross, PRL 117, 193001 (2016)]. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S02.00002: Globally-Optimized Local Pseudopotentials for (Orbital-Free) Density Functional Theory Simulations of Liquids and Solids Beatriz Gonzalez del Rio, Johannes Dieterich, Emily Carter Orbital-free density functional theory (OFDFT) is a promising technique for accurate, large-scale, quantum simulations. One key element determining the fidelity of OFDFT is the need to use local pseudopotentials (LPSs) to describe electron-ion interactions. We developed a global optimization strategy for LPSs that enables OFDFT to reproduce solid and liquid properties obtained from Kohn-Sham DFT, resulting in globally optimized LPSs (goLPSs) that can be used in solid- and/or liquid-phase simulations, depending on the fitting process.1 Moreover, we can improve the initial transferability of goLPSs by fitting to the delta-gauge2 and the valence electron density in the solid phases. A variety of test cases show that we can (1) improve solid properties compared to our previous bulk-derived LPS generation scheme; (2) refine predicted liquid and solid properties, as well as phase transition temperatures, by adding force-matching data; and (3) generate accurate goLPSs directly from the local channel of non-local pseudopotentials. We also will introduce the new goLPS library available. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S02.00003: van Leeuwen Theorem for Mixed States and Finite Temperature Density Response James Dufty, Kai Luo, Sam Trickey A simple proof of the van Leeuwen theorem for existence and uniqueness of v-representability in finite-temperature time-dependent density functional theory is described. It is used to construct the linear density response function for a system of electrons in a random configuration of ions, in terms of its corresponding non-interacting form. The relevance of this for justifying the Kubo-Greenwood model for transport properties in warm, dense matter, and its context, is described. The density response function in the "adiabatic approximation" is shown to be the same as that from a recent exact short time kinetic theory [1]. This provides a further characterization of that approximation, and makes connection to the many-body methods of kinetic theory. 1. On the Kubo-Greenwood Model for Electron Conductivity, J. Dufty, J. Wrighton, K. Luo, and S. Trickey, submitted to Contr. Plasma Phys., arXiv:1709.04732. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S02.00004: Even-handed subsystem selection in projection-based wavefunction-in-DFT embedding Matthew Welborn, Thomas Miller Projection-based embedding offers a simple framework for embedding wavefunction theories in density functional theory. Underlying this embedding is a heuristic for translating the chemically-intuitive idea of a set of embedded atoms into a set of embedded orbitals on which the wavefunction calculation will be performed. For single-point energy calculations, a successful heuristic has been to first localize the occupied Kohn-Sham orbitals, and then assign these localized orbitals to the embedded region based on atomic population analysis. However, for chemical reactions involving large geometry changes, the nature of the localized orbitals—as well as their atomic populations—can change dramatically. This can lead to qualitatively different embedded orbitals between geometries, resulting in unphysical cusps and even discontinuities in the potential energy surface. In this talk, we present an even-handed framework for localized orbital partitioning that ensures invariance of the span of the embedded orbitals throughout a geometry coordinate. We illustrate this problem and its solution with a simple example of an SN2 reaction. We then apply our method to a nitrogen umbrella flip in a cobalt-based CO2 reduction catalyst and to the binding of CO to a Cu(111) surface. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S02.00005: A study of accurate exchange-correlation functionals through adiabatic connection Manoj Harbola, Rabeet Singh A systematic way of improving exchange-correlation energy functionals of density functional theory has been to make them satisfy more and more exact relations. Starting from the initial GGA functionals, this has culminated into the recently proposed SCAN(Strongly constrained and appropriately normed) functional that satisfies several known constraints and is appropriately normed. The ultimate test for the functionals developed is the accuracy of energy calculated by employing them. In this paper, we test these exchange-correlation functionals - the GGA hybrid functionals B3LYP and PBE0, and the meta-GGA functional SCAN - from a different perspective. We study how accurately these functionals reproduce the exchange-correlation energy when electron-electron interaction is scaled as Vee with varying between 0 and 1. Our study reveals interesting comparison between these functionals and the associated difference Tc between the interacting and the non-interacting kinetic energy for the same density. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S02.00006: Development of Effective Stochastic Kohn-Sham Potential Method using Random Matrix Theory for Performing DFT Calculations on Noisy Chemical Systems Arindam Chakraborty In this work, we present the effective stochastic Kohn-Sham (ESKS) potential method to address the fundamental question of the impact of fluctuations in the external potential in the KS-DFT formulation. The functional relationship between the external potential and the electron density is central to the DFT formulation. Need for efficient treatment fluctuations in the external potential arises in chemical systems because of the presence of solvents and the existence of non-zero temperatures. We introduce the concept of a deformation potential and demonstrate its existence by the proof-by-construction approach. A statistical description of the fluctuations in the deformation potential due to non-zero temperature was obtained using infinite-order moment expansion of the distribution. The formal mathematical definition of the effective stochastic Kohn-Sham potential was derived using functional minimization approach to match the infinite-order moment expansion for the deformation potential. Practical implementation of the ESKS was obtained using the random-matrix theory method. The developed method was applied for calculations of the distribution of energies and quasiparticle gaps in atoms, molecules, and solvated quantum dots at non-zero temperatures. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S02.00007: Strong correlation in time-dependent density functional theory Kieron Burke, Diego Carrascal, Jaime Ferrer, Neepa Maitra The asymmetric Hubbard dimer is used to study the density-dependence of the exact frequency- dependent kernel of linear-response time-dependent density functional theory (TDDFT). The exact form of the kernel is given, and the limitations of the adiabatic approximation utilizing the exact ground-state functional are shown. A generalization of the double-excitation kernel of dressed TDDFT is derived for this situation, and shown to be accurate in the weak-correlation regime. A simple interpolation of the kernel between carefully defined weak-correlation and strong-correlation regimes yields accurate transition frequencies for both the single and double excitations, including charge-transfer excitations. A general definition of multiple excitations is given. Oscillator strengths are defined appropriately for lattice Hamiltonians. The exact fluctuation-dissipation formula for the ground-state XC energy for the dimer is given. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S02.00008: Fluctuations in density-functional theory for fluids: Theory and computations Miguel Angel Duran-Olivencia, Petr Yatsyshin, Antonio Russo, Serafim Kalliadasis Classical density-functional theory (DFT) for fluids and its dynamic extension (DDFT) provide an appealing mean-field framework for describing equilibrium and dynamics of complex soft matter systems. For a long time, accounting for the effects of thermal fluctuations under this theoretical framework was thought to be impossible, if not fundamentally incorrect. Here, we present an ab-initio derivation of a fluctuating DDFT (FDDFT) where thermal fluctuations are derived from first principles, thus advancing the long-standing debate about the inclusion of fluctuations. As a by-product, we obtain a non-equilibrium energy functional which recovers the Helmholtz free energy under equilibrium conditions. We show that there is a one-to-one connection between our FDDFT formalism and the phenomenological Landau-Lifshitz fluctuating hydrodynamics. To showcase the potential and computational capacity of the formalism developed in this work, we apply it to the study of homogeneous nucleation, a classical problem considered to be outside the limits of applicability of DFT. Finally, we highlight how our theoretical effort can open the door to the discovery of new physical laws governing the dynamics of soft-matter systems out-of-equilibrium and under noise-dominated conditions. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S02.00009: Understanding interfacial wetting transitions with classical density functional theory Petr Yatsyshin, Miguel Angel Duran-Olivencia, Andrew Parry, Carlos Rascon, Serafim Kalliadasis Interfaces provide valuable insights into the workings of the atomic world. In problems of wetting, where often a liquid-gas interface is in contact with a solid substrate, the width and position of the gas-liquid interface depend strongly on the range of interparticle potentials. A satisfactory description of wetting can be achieved by classical density-functional theory (DFT), a fully microscopic approach, capturing the small-scale behavior of matter, as well as the inherently non-local nature of interparticle interactions. In this talk, we apply classical DFT to investigate small-scale surface phase transitions in a wide spectrum of physical settings with emphasis on wetting on heterogeneous planar substrates. We compute wetting isotherms, locating hystereses and the jumps in adsorption, wetting temperatures and interface binding potentials (disjoining pressure). Our results may have important ramifications for the design of lab-on-a-chip devices, superhydrophobic surfaces, and controlled micro-/nanofluidics. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S02.00010: Zero-point motion of molecules: beyond Born-Oppenheimer Grigory Kolesov, Efthimios Kaxiras, Efstratios Manousakis We have recently developed a new time-dependent density-functional theory (TDDFT)-based non-Born-Oppenheimer method for computing electron-ion structure of atomistic systems in the path integral formalism. We discuss our implementation of this exact (within the accuracy of DFT) method with a localized basis set approach. The method and the implementation can be used for both molecules and solids. First we apply this method to compute electron-ion states and zero-point energies of small molecules. Next we compare the results of these computations to results obtained from the standard (Born-Oppeheimer-based) path-integral methods used in the field. We demonstrate that at low temperatures the error of the standard path-integral approaches is large even for the systems with wide bandgaps. We discuss potential areas of applicability of our method. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S02.00011: Efficient Implementation of the Approximate Exchange Kernel Method Guo Chen, Matthew Agee, Filipp Furche The approximate exchange kernel (AXK) method is the leading correction to the random-phase approximation (RPA) for the ground-state correlation energy functional within RPA-renormalized many-body perturbation theory. AXK alleviates the unphysical short-range behavior of RPA and improves the prediction of energetics for processes that do not conserve the number of electron pairs. However, the relatively high computational cost of AXK has hampered its widespread application in the past. Here we present a fast AXK algorithm with O(N4lnN) scaling. The algorithm takes advantage of the resolution-of-the-identity (RI) approximation and imaginary frequency integration technique. The new RI-AXK implementation in TURBOMOLE enables correlation energy calculations for molecules with well over 100 atoms on a single cluster node. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S02.00012: The SCAN Meta-GGA : An Efficient Universal Non-Empirical Semi-local Density Functional Jianwei Sun The accuracy of the Kohn-Sham density functional theory is limited by the approximation to its exchange-correlation energy Exc. Due to the computational efficiency of semi-local approximations that use as inputs only the electron density, its gradient, and the kinetic energy density, efforts are still made to improve the PBE GGA, the standard non-empirical semi-local density functional that is robust and universally applicable to different systems. Semi-local approximations are also bases for developing non-local density functionals that are needed for treating long-range effects (e.g., the van der Waals interaction and charge transfer), which further motivates such efforts. The SCAN semi-local density functional, the most sophisticated one so far [1] with systematic improvement over PBE with a comparable computational efficiency[2], represents a successful example of these efforts. Here, SCAN is further tested and gives promising performance on two difficult properties: the ground structure selections of about 300 binary solids and the metal-insulator-transition of a cuprate under doping. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S02.00013: A Novel Generalized Gradient Approximation for the Non-interacting Kinetic Energy Density Functional Kai Luo, Valentin Karasiev, Sam Trickey Reliable and accurate approximation of the non-interacting kinetic |
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