Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P39: First-Principles Modeling of Excited-State Phenomena in Materials VIII: TDDFT and Nonadiabatic DynamicsFocus
|
Hide Abstracts |
Sponsoring Units: DCOMP DMP DCP Chair: David Strubbe, University of California, Merced Room: 703 |
Wednesday, March 4, 2020 2:30PM - 3:06PM |
P39.00001: Heterogeneous proton-coupled electron transfer at nanoparticle and electrode interfaces Invited Speaker: Sharon Hammes-Schiffer Interfacial proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of energy conversion processes. A general theory of PCET that includes the quantum mechanical effects of the active electrons and transferring protons, as well as the motions of the proton donor-acceptor mode and solvent environment, has been developed. This formulation enables the calculation of rate constants and kinetic isotope effects for homogeneous as well as heterogeneous processes at nanoparticles and electrode surfaces. This theory has been applied to experimentally studied photoreduced ZnO nanocrystals reacting by PCET with the nitroxyl radical TEMPO. The calculations indicate that the electron transfers from the conduction band of the ZnO nanocrystal to TEMPO concertedly with proton transfer from a surface oxygen of the ZnO nanocrystal to the oxygen of TEMPO. Proton diffusion from inside the nanocrystal to reactive sites on the surface was found to explain the experimentally observed nonexponential kinetics. This PCET theory has also been applied to experimentally studied proton discharge from triethylammonium to a gold electrode in acetonitrile. These experiments demonstrated an isotope-dependent Tafel slope or, equivalently, a potential-dependent kinetic isotope effect. The calculations explain the potential-dependent kinetic isotope effect in terms of contributions from excited electron-proton vibronic states that depend on both isotope and applied potential. Proton discharge to a gold electrode in acidic and alkaline aqueous solution has also been studied. These applications highlight the importance of using a vibronically nonadiabatic theory that quantizes the transferring proton and includes the effects of hydrogen tunneling and excited electron-proton vibronic states. These studies are also assisting in the interpretation of experimental data and the design of more effective catalysts for energy conversion processes. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P39.00002: Excitation Dynamics in Water under Proton Irradiation: Time-dependent Maximally-Localized Wannier Function Approach Chris Shepard, Dillon C Yost, Yi Yao, Yosuke Kanai Proton irradiation of liquid water has many important medical applications, including proton beam therapy. However, understanding the quantum dynamical details of the electronic excitations of water induced by the energetic protons has long been intangible. Using the approach of propagating maximally localized Wannier functions (MLWFs) in real-time TDDFT, we study the molecular-level dynamics of the electronic excitations1. These time-dependent MLWFs (TD-MLWFs) are localized in space, offering a convenient ‘chemical moiety’ picture of liquid water and allow for understanding of the electron dynamics in terms of bond centered and lone pair electrons of water molecules. The spatially-localized nature of the TD-MLWFs allows us to study the secondary electronic excitations from the electrons initially excited by the proton. The MLWF gauge also enables usage of the length-gauge to describe the homogeneous electric field to model photo-excitation, and analyze proton and photo- irradiation on equal footing. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P39.00003: Time-dependent exciton wave functions from TDDFT Jared R. Williams, Carsten A. Ullrich Time-dependent density-functional theory (TDDFT) is a computationally efficient alternative to the Bethe-Salpeter equation for calculating optical spectra in insulators and semiconductors, including excitonic effects. We show how time-dependent exciton wave functions can be obtained from TDDFT via the time-dependent Kohn-Sham transition density matrix. The method is illustrated using one-dimensional model solids. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P39.00004: Transient X-ray absorption spectra in solids from generalized Kohn-Sham real-time TDDFT. Sri Chaitanya Das Pemmaraju Simulating transient X-ray absorption spectra in solids with TDDFT requires at a minimum, a balanced treatment of both localized core and possibly delocalized valence excitations. To this end range-separated hybrid exchange-correlation functionals offer improved accuracy by mitigating self-interaction errors across multiple length-scales [1,2]. In this work the velocity-gauge formulation of real-time TDDFT is combined with multiply-range-separated hybrid functionals to simulate transient soft X-ray near-edge absorption spectra in solids where excitonic effects are important. Immediately following laser excitation by few femtosecond pump pulses, soft X-ray probe spectra are shown to exhibit characteristic features of population induced bleaching and transient energy shifts of exciton peaks. Simulation results are assessed for accuracy by comparison with experimental data on prototypical solid state systems. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P39.00005: TD-DFT without wavefunctions Kaili Jiang, Xuecheng Shao, Michele Pavanello We present an extension of Orbital-Free Density Functional Theory (OFDFT) to the time domain (TD-OFDFT). The method hinges upon approximating the wavefunction of the system by a single effective orbital augmented by a position-dependent phase factor. We find that such a simplified picture still delivers good optical spectra and response properties for metal clusters, surfaces and bulk systems. Specifically, we show that the method delivers plasmonic collective electronic excitations of metal clusters in reasonable agreement with Kohn-Sham TD-DFT. Because of the simplicity of the model, and the efficient codebase [1], the simulations are extremely computationally efficient delivering converged results in wall-times two or more orders of magnitude smaller than conventional Kohn-Sham TD-DFT. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P39.00006: Pre-equilibrium stopping power mechanisms in proton-irradiated aluminum sheets Alina Kononov, Andre Schleife Although ion-irradiation is a standard tool for imaging and altering materials' surfaces, most existing knowledge concerning an energetic ion's interaction with solids is limited to bulk materials. As an ion approaches and traverses a surface, it is expected to exchange charge with the material and transition into bulk conditions resembling a steady-state. To gain insight into this so-called pre-equilibrium behavior, we use real-time time-dependent density functional theory to simulate protons with 6 - 60 keV of kinetic energy impacting few-layer aluminum sheets. We find up to 25% stopping power enhancement in aluminum sheets compared to bulk, particularly near the entrance surface, and we examine several possible explanations for this behavior including pre-equilibrium projectile charge dynamics, polarization induced in the sheet during the proton's approach, and surface plasmon excitations. Our analysis suggests that surface plasmons are a plausible source of stopping power enhancement, while the contribution of the other potential mechanisms is either small or inconclusive. Such pre-equilibrium behavior has particularly important implications for optimizing focused ion beam techniques for 2D materials. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P39.00007: Quantitative electronic stopping power from localized basis set Ivan Maliyov, Xixi Qi, Jean-Paul Crocombette, Fabien Bruneval In charged particle irradiation, the electronic excitations are the prevailing phenomenon. The energy transfer from the projectile to the electrons of the target material is measured by the so-called electronic stopping power. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P39.00008: New Simulation Method for Temperature Dependent Magnetic Circular Dichroism with Non-Perturbative Treatment of Magnetic Field Shichao Sun, Xiaosong Li Magnetic circular dichroism (MCD) is an important experimental tool for probing open shell molecules, but the simulation is challenging. First, simulating MCD involves multiple perturbations, such as magnetic field, spin-orbit coupling and circularly polarized light. Second, the ground state Zeeman splitting comparable with kT makes MCD temperature dependent. Scientists used to parameterize temperature dependence, and evaluate the perturbation by sum over states or excited state gradient method. However, such perturbations increase the computational cost and fail in strong magnetic field. We developed a non-perturbative treatment of magnetic fields and spin-orbit coupling in linear response non-collinear TDDFT formalism, which simplifies the perturbation. It is especially advantageous for strong magnetic field. In order to resolve the temperature dependence of MCD, excitations are weighted by temperature dependent occupation number. This method is applied in Mo(CN)83- and gives correct MCD-temperature dependence. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P39.00009: Polarization dependence of optical excitations in anisotropic metal/insulator heterostructures Markus Ernst Gruner, Rossitza Pentcheva In the framework of real-time time-dependent density functional theory (RT-TDDFT) we unravel the layer-resolved dynamics of a Fe1/(MgO)3(001) multilayer after optical excitations. Short optical pulses with two polarization directions of light and a frequency smaller than the band gap of bulk MgO induce strongy anisotropic dynamic response: Substantial transient changes to the electronic structure, which persist after the duration of the pulse, are only observed for in-plane polarized electric fields. We find the largest effect in the Fe-layer, but time-dependent changes in the occupation numbers are visible in all layers, promoted by the presence of interface states. The time evolution of the layer-resolved occupation numbers indicates transfer from in-plane to out-of-plane orbitals that support the propagation of optically induced excitations into the interface region. We also see a small net charge transfer away from oxygen towards the Mg sites even for MgO layers, which are not directly in contact with the metallic Fe. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P39.00010: Dissociation Path Competition of Radiolysis-Ionization induced Molecule Damage under Electron Beam Illumination Zenghua Cai, Shiyou Chen, Lin-Wang Wang The radiolysis ionization under electron beam illumination induces dissociation and damage of organic and biological molecules, which causes the inability of transmission electron microscopy (TEM) in imaging the related materials. We developed a procedure based on the real-time time-dependent density functional theory (rt-TDDFT) for simulating the radiolysis damage processes of molecules, which can describe the ionization cross sections of electronic states and the fast dissociation processes caused by the hot carrier cooling and the Auger decay on deep levels. For the radiolysis damage of C2H6O2, our simulation showed unexpectedly that there is strong competition among three different dissociation paths, including the fast dissociation caused by the hot carrier nonadiabatic cooling; the fast dissociation caused by Auger decay induced double ionization and Coulomb explosion; the slow dissociation caused by the increased kinetic energy. As the energy of incident electron beam changes, the time scales of these dissociation paths and their prudency in causing the molecule damage change significantly. These results explained the measured mass spectra of the C2H6O2 dissociation fragments, and revealed the dissociation paths in the TEM imaging of organic and biological materials. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P39.00011: Generalized nanoquanta exchange-correlation kernel and nonhydrogenic Rydberg series of excitonic binding energies in monolayer WS2 Volodymyr Turkowski, Jose Mario Galicia-Hernandez, Gregorio Hernandez-Cocoletzi, Talat S. Rahman We have formulated a methodology to derive a generalized nanoquanta (nanoquanta+) TDDFT exchange-correlation (XC) kernel that is capable of describing excitonic properties of extended systems. Compared to the standard nanoquanta XC kernel, the generalized one takes into account screening effects more accurately through the usage of exact (beyond one-loop) electron susceptibility in the formalism. As we demonstrate for the example of monolayer WS2, such an improved XC kernel allows one to reproduce accurately the experimentally-observed nonhydrogenic Rydberg series in the excitonic spectrum, [1] which has so far not been possible with other familiar kernels. We also calculate the effective electron-hole potential that enters the TDDFT eigen-energy equation of excitons, and demonstrate that the reason for the nonhydrogen Rydberg energy series is a non-Coulomb structure of the potential. We discuss the general properties of the nanoquanta+ kernel and compare them to that of other XC kernels employed for extracting properties of excitons. |
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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700