Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W26: Computational Applications and Methods II |
Hide Abstracts |
Sponsoring Units: DCP Chair: Ryan Steele, University of Utah Room: 204A |
Thursday, March 5, 2015 2:30PM - 2:42PM |
W26.00001: Spin-Polarized Nonadiabatic Dynamics with Local Basis Sets Robert Hoyt, Grigory Kolesov, Georgios Tritsaris, Oscar Granas, Efthimios Efthimios Accurate simulations of electron transfer at the solid-electrolyte interphase (SEI) are critical for understanding and predicting electrochemical reactions. Density-Functional Theory (DFT) has been widely applied to study the ground-state structure of novel materials for electrochemical energy storage and for adiabatic molecular dynamics. Unfortunately, many chemical reactions take place on femtosecond time scales where assuming adiabatic electron density propagation is invalid. To resolve this, we have developed the ability to perform time-dependent DFT calculations using nonadiabatic propagation of the electron density along with Ehrenfest dynamics for the ions to better capture the complex interactions that occur during surface-electrolyte electron transfer and chemical reactions. Spin polarization is also implemented to improve the accuracy of the simulations and their suitability for studying a wider range of chemical reactions. Local basis sets are implemented via linear combinations of atomic orbitals to reduce the size of the DFT basis for computational efficiency. [Preview Abstract] |
Thursday, March 5, 2015 2:42PM - 2:54PM |
W26.00002: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 2:54PM - 3:06PM |
W26.00003: Ultrafast Electron-Ion Dynamics Near Aluminum Surfaces Andre Schleife, Kai Wells, Sam Knewstub Computational physics and materials research have greatly benefited from high-performance computing; modern first-principles simulations allow insight with unprecedented accuracy and detail. Here we use a recent highly parallel implementation of Ehrenfest molecular dynamics based on real-time time-dependent density functional theory to describe non-adiabatic ultrafast electron-ion dynamics using accurate first-principles calculations. We investigate aluminum subject to highly energetic particle radiation (hydrogen projectile) and study energy deposition due to the fast projectiles. Their high velocity makes it necessary to overcome the Born-Oppenheimer approximation. Using our first-principles calculations we study the behavior of fast ions near the surface of aluminum slabs and investigate, for instance, the influence of velocity and impact angle of the projectile ion. From the emerging non-adiabatic electron-ion dynamics we gain insight into the material on an atto-second time scale. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W26.00004: New spectroscopic approaches for periodic systems Sandra Luber Knowledge about local properties is extremely helpful for the analysis of structures and interactions. Moreover, it is a valuable source of information for the characterisation of dynamic processes and facilitates the interpretation of experimental data. In case of vibrational spectroscopy, for example, it is desirable to determine the impact of certain atoms/molecules on the bands in the experimental spectra. This may be straight forward for small systems but becomes more and more complex for larger systems. Calculations provide additional insight allowing the targeted study of specific structures. In this way, it is possible to quantify the contributions of, for instance, solute and solvent molecules [1] or adsorbates on solids. We present novel, computationally efficient methods for the calculation of properties for periodic systems such as liquids and solids. These are applied to calculate, among others, vibrational spectra via ab initio molecular dynamics [2,3]. References: [1] S. Luber, J. Phys. Chem. A 117 (2013) 2760. [2] S. Luber, M. Iannuzzi, J. Hutter, J. Chem. Phys. 141 (2014) 094503. [3] S. Luber, submitted. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W26.00005: Polarons in rutile TiO2 surfaces: a non-adiabatic excited-state dynamics study Grigory Kolesov, Dmitry Vinichenko, Georgios Tritsaris, Cynthia Friend, Efthimios Kaxiras Titanium dioxide is one of the most thoroughly studied photocatalytic materials with numerous proposed applications ranging from hydrogen production to cleanup of environmental pollutants. Photocatalytic methoxy splitting on rutile TiO2 (110) surfaces that leads to formation of formaldehyde has been previously observed in STM and TPD experiments. Due to complexity of such photocatalytic reactions the computational simulations of these reactions are requisite for providing insight into their underlying mechanisms and are crucial for the rational design of the new photocatalysts. Because such simulations are necessarily computationally expensive we developed an efficient methodology based on time-dependent density functional theory (TDDFT) and localized basis set. Our recent non-adiabatic simulations of the photo-catalytic methoxy splitting on titania surface demonstrate an extremely important role played in these reactions by surface and subsurface polarons. Here the polarons serve as electron acceptor sites that participate in driving the reaction and are required to stabilize the reaction products and allow for their subsequent desorption from the surface. In this work we focus on the polarons in rutile titania surfaces and study dynamics of their formation and their properties. [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W26.00006: TDDFT+DMFT analysis of excitations and relaxation dynamics in alpha-Ce Syed Islamuddin Shah, Volodymyr Turkowski, Talat S. Rahman We apply a combination of time-dependent density functional theory and dynamical mean-field theory (TDDFT+DMFT) to study the excitation spectrum and response of bulk alpha-Ce to an external perturbation by a laser pulse. The excitation spectrum is obtained by solving TDDFT Casida equation with the ``free electron'' spectrum calculated from density functional theory and the exchange-correlation (XC) kernel extracted from the DMFT charge susceptibility. We pay special attention to the complex role of the hybridization of the f- with the s-, p-, and d-electron states in the system spectrum. The nonequilibrium solution of the TDDFT equations shows that the short-lived local moments of f-electrons get suppressed as the hybridization strength between the f- and other orbitals increases. We also calculate the effective scattering times for the scattering of the f-electrons from the s-, p-, and d-states at different values of the local Coulomb repulsion and exchange J parameters from the corresponding expression for the orbital-resolved XC kernel, and analyze how these scattering processes may affect the dynamics of the system relaxation. [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W26.00007: Auger Relaxation of Hot Electrons in CdSe Quantum Dots using GFSH Dhara Trivedi, Linjun Wang, Oleg Prezhdo We carry out \textit{ab initio} nonadiabatic molecular dynamics (NAMD) simulations to study the fast relaxations of hot electrons in a CdSe quantum dot (QD). The reviewed system is a promising candidate for QD-sensitized semiconductor solar cells and the presence of well-separated conduction electron states opens the possibility of energy selectivity for hot carriers. We examine the intraband relaxation of the photoexcited electrons in the QD and the role of surface ligand in the process. A novel global flux surface hopping (GFSH) approach is adopted. We investigate the electron relaxation from the 1Pe to 1Se state in pure and 1,6-hexanedithiol ligated CdSe QD. The intraband relaxation is accelerated due to the Auger-type relaxation in the pure QD. The ligand forms a hole trapping state, which competes with the Auger-type relaxation impeding the electron-hole energy exchange. The present study establishes the basic theoretical model describing the relaxation processes in both scenarios. The model is supported by computational studies of relaxation dynamics in model QD-ligand complexes. The obtained interplay between the competing phonon-assisted Auger and ligand-induced trapping mechanisms has given us a comprehensive picture of the complex photoinduced dynamic related to QDs. [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W26.00008: New Developments in Ab Initio Multiple Spawning for Efficient Nonadiabatic Molecular Dynamics Basile F.E. Curchod, Aaron Sisto, David R. Glowacki, Todd J. Mart\'{I}nez Ab initio multiple spawning (AIMS) describes the nonadiabatic dynamics of nuclear wavepackets by means of a linear combination of frozen Gaussians. While the Gaussian centers follow classical trajectories, the expansion coefficients are propagated according to the time-dependent Schr\"{o}dinger equation. As a result of the coupling between Gaussian functions, AIMS accurately describes coherence and decoherence effects close to nonadiabatic regions. This accuracy has further been validated by the excellent agreement reported between AIMS dynamics and experimental observations. In this Contribution, we will discuss new techniques used to extend the applicability of AIMS to (i) larger molecules, (ii) long-time simulations, and (iii) dynamics involving an important number of electronic states. We will present different examples of nonadiabatic molecular dynamics in organic and atmospheric photochemistry, resulting from the interface between AIMS and the GPU-accelerated electronic structure code TeraChem. New methods improving the AIMS efficiency for larger systems will be discussed, such as the stochastic-selection AIMS. Finally, we will highlight early results on the extension of AIMS to the combined description of both internal conversion and intersystem crossing phenomena. [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W26.00009: Effects of Thermal and Quantum Fluctuations on Dipole-moment distribution of $H_2O$ molecules in ice $I_h$ Pedro Moreira, Maurice de Koning Molecular dipole moments are the fundamental entities that underpin the dielectric behavior of molecular materials. Here, we discuss the molecular-dipole distributions of water molecules in ice $I_h$, considering the roles of proton-disorder, as well as the effects of thermal and quantum fluctuations. For this purpose we employ \textit{ab initio} Born-Oppenheimer and Path-Integral Molecular Dynamics simulations and compute molecular dipole moments using maximally-localized Wannier functions. We discuss trends in the dipole-moment distributions as a function of temperature. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W26.00010: Screened Hybrid Exact Exchange Schemes to Adsorption Energies on Perovskite Oxides Elton Santos, Aleksandra Vojvodic, Jens K. Norskov The bond formation between an oxide surface and oxygen, which is one of the important intermediates for oxygen evolution reaction, is investigated using hybrid functionals. We show that there exists a linear correlation between the adsorption energies of oxygen on LaMO3 (M$=$Sc-Cu) oxides at hybrid calculations to those computed using semilocal density functionals through the magnetic properties of the bulk phase. The energetics of the spin-polarized surfaces follow the same trend as corresponding bulk systems, which can be treated at a much lower computational cost. The difference in adsorption energy due to magnetism is linearly correlated to the magnetization energy of bulk, i.e., the energy difference between the spin-polarized and the non spin-polarized solutions. This suggests that one could estimate the correction to the semilocal density functional adsorption energies directly from the hybrid bulk magnetization energy. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W26.00011: Kinetic compensation effect in thermal desorption Nayeli Zuniga-Hansen, Leonardo E. Silbert, Mercedes Calbi The parameters which characterize the rates of many thermally activated processes are often extracted using the Arrhenius equation. A series of closely related thermally activated processes exhibit systematic variations in the energies of activation, Ea, and preexponential factor, ?, in response to a perturbation, which leads to the concept of `kinetic compensation', such that the different parameters in the Arrhenius equation balance each other out thereby leading to an implicitly assumed constant rate. However, the compensation effect has not been generally demonstrated and its origins are not completely understood. Using kinetic Monte Carlo simulations on a model interface, we explore how site-adsorbate and adsorbate-adsorbate interactions, and surface structural changes influence surface coverage and the kinetic parameters during a typical temperature programmed desorption process. We find that the concept of the compensation effect for interacting species breaks down and the time characterizing desorption increases with increasing interaction strength due to an increase in the effective activation energy. At the `molecular' level the changes are the result of enhanced site correlations with increasing adsorbate interaction strength suppressing the onset of desorption. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W26.00012: First principles molecular dynamics simulations of the static, dynamic and electronic properties of the liquid silver-tin alloy Lazaro Calderin, David Gonzalez, Luis E. Gonzalez We report an ab-initio molecular dynamics study of several structural and dynamic properties of the liquid Ag-Sn alloy at three concentrations and a temperature of 1273 K. The calculated structural results show good agreement with the available experimental data and accurately reproduce the measured total static structure factors [1]. The heterocoordinating tendencies in the alloy have been analyzed in terms of some short range order parameters. As for the dynamical properties, the single particle dynamics in the liquid alloy has been studied by evaluating several velocity correlation functions and the associated diffusion coefficients. Results are also reported for other transport coefficients, such as the adiabatic sound velocities and shear viscosities. Finally, from the spectra of the longitudinal current correlation functions, the longitudinal dispersion curves have been computed. [1] I Kaban, W Hoyer, A Ilinski, O Slukhovskii and S Slyusarenko, J. Non-Cryst. Solids, 331, 254-262 (2003) [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W26.00013: Orbital-free ab initio molecular dynamics study of the free liquid surface of Sn. From pseudopotential generation to structural and dynamic properties Beatriz Gonzalez del Rio, Luis Enrique Gonzalez Tesedo We report results of an orbital-free ab initio molecular dynamics (OF-AIMD) study of the free liquid surface of Sn at 1000 K. A key ingredient in the OF-AIMD method is the local ionic pseudopotential describing the ions-valence electrons interaction. We have developed a force-matching method [1] to derive a local ionic pseudopotential suitable to account for a rapidly varying density system, such as in a free liquid surface. We obtain very good results for several structural properties. We have also studied the evolution of some dynamical properties when going from the central region (where the system behaves like the bulk liquid) towards the free liquid surface.\\[4pt] [1] B.G. del Rio and L.E. Gonzalez, J.Phys.:Condens. Matter 26, 465102 (2014) [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W26.00014: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W26.00015: ABSTRACT WITHDRAWN |
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