Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T46: Excited State V: real time TDDFTFocus Recordings Available

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Sponsoring Units: DCOMP DMP Chair: Yuan Ping, UC Santa Cruz Room: McCormick Place W470A 
Thursday, March 17, 2022 11:30AM  12:06PM 
T46.00001: Exactfactorizationbased methods for coupled electrons, ions, and photons. Invited Speaker: Neepa T Maitra The description of excited state phenomena requires both an adequate description of the electronic structure and electronnuclear correlation, while calling for computationally efficient methods to deal with the size and complexity of the systems of interest. This talk focusses on the electronnuclear correlation problem within the exact factorization (XF) framework, which provides exact potentials that drive different coupled quantum subsystems, and, more practically, provides a rigorous starting point for approximate methods. We show that XFderived modifications to the surfacehopping equations contain terms that correctly lead to population transfer and decoherence, while retaining a computationallyefficient independent trajectory picture, with particularly improved predictions of nonadiabatic dynamics when several electronic states become coupled. We further discuss the extensions of these methods to polaritonic systems where strong lightmatter coupling through confinement modifies the chemical and physical properties of matter. Finally, the exact potential driving the photons is used to analyze the accuracy of Ehrenfest methods adapted to account for many photon modes. 
Thursday, March 17, 2022 12:06PM  12:18PM 
T46.00002: A novel TransitionBased Constrained DFT (TCDFT) for the Robust and Reliable Treatment of Pure and Mixed Excitations in Molecular Systems. Martina Stella, Laura E Ratcliff, Luigi Genovese, Kritam Thapa Despite the variety of available computational approaches, stateoftheart methods for calculating excitation energies such as timedependent density functional theory (TDDFT), are typically computationally demanding and thus limited to moderate system sizes. We present a new variation of constrained DFT (CDFT), implemented in the BigDFT code, wherein the constraint corresponds to a particular transition (T) between occupied and virtual orbitals, rather than a region of the simulation space as in traditional CDFT. We perform benchmark TCDFT calculations for a set of gas phase acene molecules and OLED emitters considering both pure and mixed excitation states. For both classes of molecules, we find that TCDFT based on semilocal functionals is comparable to hybrid functional results from ΔSCF and TDDFT. Furthermore, TCDFT proves to be more robust than ΔSCF and does not suffer from the wellknown problems encountered when applying TDDFT to chargetransfer (CT) states, and is therefore applicable to both local excitations and CT states. Finally, TCDFT is designed for large systems and it is ideally suited for exploring the effects of explicit environments on excitation energies, paving the way for future simulations of excited states in complex realistic morphologies. 
Thursday, March 17, 2022 12:18PM  12:30PM 
T46.00003: Cumulative Surface Hopping: Faster and More Reproducible Colin Schiltz, Shane M Parker Photochemistry simulations powered by trajectory surface hopping (TSH) dynamics have become an essential tool for understanding lightdriven reactivity. In TSH, electronic transitions are mimicked using stochastic hops between electronic surfaces and the statistics of hopping are sampled using independent trajectories. In the conventional approach to TSH, hops are determined by comparing the instantaneous hopping probability to a random number at each time step. Here, we describe an alternative scheme using the cumulative hopping probability. We will show how this seemingly simple alteration opens the door to semistochastic sampling algorithms that drastically reduce computational time, and new strategies to numerically evaluate propagation algorithms, all while improving computational reproducibility. We argue that using cumulative hopping probabilities has myriad advantages over the conventional approach and no apparent disadvantages. Thus, we recommend cumulative surface hopping as the default approach in all TSH implementations. 
Thursday, March 17, 2022 12:30PM  12:42PM 
T46.00004: Fast allelectron realtime TDDFT calculations for electronic stopping power Xixi Qi, Ivan Maliyov, JeanPaul Crocombette, Fabien Bruneval Swift ions traveling through matter are slowed down due to electronic excitations. The electronic stopping power quantifies this phenomenon and is central to the aging of functional materials in nuclear or space environments [1]. Confronted with the heavy computational cost of realtime timedependent densityfunctional theory (RTTDDFT) approaches, we have developed a fast alternative using localized Gaussiantype orbitals [2, 3]. Our program has been successfully applied to both metal [3] and insulator [4] targets, however only for projectile ions totally stripped of their electrons. 
Thursday, March 17, 2022 12:42PM  12:54PM Withdrawn 
T46.00005: On stationary solutions for the electronic stopping of projectiles in solids Marjan Famili, Emilio Artacho, Jessica Halliday The recent proposal of a Floquet theory of electronic stopping along periodic directions in crystalline solids indicates the existence of stationary solutions for the electronic stopping problem. Some properties are predicted to be time periodic (or stroboscopically constant, as the electronic stopping power itself), while other have timeperiodic time derivatives (spectral decompositions). Taking advantage of largecell realtime timedependent densityfunctional theory simulations, we explore such properties in the electronic stopping of protons in large supercells of diamond and compare them to metal hosts. We explore the velocity and direction dependence of electronic stopping power in this crystal. 
Thursday, March 17, 2022 12:54PM  1:06PM 
T46.00006: FirstPrinciples Methods for Simulating Inelastic Scattering of High Energy Electron Beams by Materials David B Lingerfelt, Jacek Jakowski, Panchapakesan Ganesh, Bobby G Sumpter 
Thursday, March 17, 2022 1:06PM  1:18PM 
T46.00007: NonLinear Dynamics of Plasmon Excitation at MetalSemiconductor Interfaces from First Principles Theory John L Bost We apply firstprinciples electronic structure calculation to study the process of plasmoninduced charge transfer that takes place between a plasmonic metal nanoparticle and semiconductor surface. Through analysis of the timedependent maximally localized Wannier functions in realtime timedependent density functional theory, we describe the excited behavior of the plasmon and the resulting effect on the interface. In this work we focus specifically on the plasmonic Ag20 nanocluster interfaced with a hydrogenated silicon surface. 
Thursday, March 17, 2022 1:18PM  1:30PM 
T46.00008: Analytical nonadiabatic exchangecorrelation potentials for nonequilibrium studies of strongly correlated materials Volodymyr Turkowski, Talat S Rahman The quest for a microscopic understanding of the ultrafast processes in strongly correlated materials hinges on the fact that it captures the role of electron correlations. To accomplish this challenging task, a way forward is through derivation of appropriate exchangecorrelation (XC) potentials for implementation in timedependent densityfunctional theory (TDDFT). We present here analytical expressions for such (nonadiabatic) potentials in the limits of strong and weak electron correlations, obtained by using the ShamSchlueter equation approach. The XC potentials are obtained from the localinspace electron selfenergy in the oneband Hubbard model. To test the potentials, we employ them in TDDFT calculations for the oneband Hubbard model and compare the results with the nonequilibrium dynamical meanfield theory solution which shows good agreement. We discuss strategies for formulation of a universal XC potential valid also for intermediate strengths of electron correlations. The net outcome is a reliable and computationally efficient XC potential that takes into account both memory and correlation effects and can be applied to examine ultrafast properties of materials at any strength of the perturbing field. 
Thursday, March 17, 2022 1:30PM  1:42PM 
T46.00009: Firstprinciples study of shift current mechanism in lowdimensional inversionbroken systems Bumseop Kim, Jeongwoo Kim, Noejung Park Bulk photovoltaic effect, characterized by the generation of a steady photocurrent without the aid of external pn junction, has attracted a lot of attention because of its potential as a highperformance solar energy harvester. We perform ab initio simulations to obtain the realtime photocurrent, and investigate underlying electronic origin of the photocurrent generation mechanism in organic molecular solids (TTFCA), hybrid halide perovskite (MAPbI3 and FAPbI3), and transition metal dichalcogenides (TMDs). We show the photovoltaic nature can be associated with the interchain charge shifting mechanism in TTFCA. For hybrid halide perovskite, though both the ferroelectric polarization and the nonzero bulk photocurrent are prototypical manifestation of the broken inversion symmetry, we investigate that the photovoltaic nature is not necessarily associated with the ferroelectricity, but is rather determined by the intrinsic electronic band properties near the Fermi level. By considering onedimensional TMD nanotubes we examine the effect of dimensionality, beyond the broken inversion symmetry, on the generation mechanism of photocurrent. We find that the nanotube structure can produce substantially larger shift current as observed in experiment. We suggest that the realtime analysis of the photocurrent can provide a better understanding of the bulk photovoltaics, beyond the widely used perturbation schemes. 
Thursday, March 17, 2022 1:42PM  1:54PM 
T46.00010: Real time electron emission dynamics of graphene under proton irradiation Yifan Yao, Andre Schleife Graphene has a wide range of applications in novel electronics devices, such as transistors, biosensors, and solar cells. However, since its properties can be sensitively influenced by its defects, a precise characterization technique is often required for materials fabrication. Focused ion beams have been widely employed in this context, but their parameters must be carefully selected, which requires a detailed understanding of the underlying excited electron dynamics. Here, we apply a combination of realtime time dependent density functional theory and Ehrenfest dynamics to qualitatively investigate the intensity and duration of secondary electron pulses for graphene under proton irradiation and its dependence on proton trajectory and velocity. We reveal that centroid trajectories yield 3853% more secondary electrons than channeling trajectories on both sides of the graphene. Also, we find that the duration of secondary electron pulses increases as the proton velocity increases. Recapture of electrons can be observed after 1 fs for protons with kinetic energy near 6.1 keV but after 3 fs for protons with kinetic energy more than 25 keV. This comprehensive description of secondary electron pulses provides critical insight into optimizing the parameters of ion beams. 
Thursday, March 17, 2022 1:54PM  2:06PM 
T46.00011: Firstprinciples studies of point defects in semiconductors using timedependent density functional theory Yu Jin, Marco Govoni, Giulia Galli Firstprinciples calculations can be used to accelerate the discovery of point defects in semiconductors and insulators, with applications for solidstate quantum technologies. However, the simulation of the optical properties of pointdefects, e.g., of photoluminescence (PL) spectra [1], is still a difficult task because it is challenging to obtain an accurate description of multiconfigurational excited potential energy surfaces of defects in solids. Here we discuss the calculations of excited states and PL spectra of defects in diamond and hexagonal boron nitride, carried out using an efficient implementation of forces at the level of timedependent hybrid density functional theory (TDDFT) for periodic systems. The comparison of our results with experiments suggests that TDDFT with hybrid functionals can be used for robust predictions of the excited state properties of point defects in semiconductors. 
Thursday, March 17, 2022 2:06PM  2:18PM 
T46.00012: FirstPrinciples Demonstration of Nonadiabatic Thouless Pumping of Electrons in a Molecular System Ruiyi Zhou, Dillon C Yost, Yosuke Kanai We demonstrate nonadiabatic Thouless pumping of electrons in transpolyacetylene in the framework of Floquet engineering using firstprinciples theory. We identify the regimes in which the quantized pump is operative with respect to the driving electric field for a timedependent Hamiltonian. By employing the timedependent maximally localized Wannier functions in realtime timedependent density functional theory simulation, we connect the winding number, a topological invariant, to a molecularlevel understanding of the quantized pumping. Using a gaugeinvariant formulation called dynamical transition orbitals, an alternative viewpoint on the nonequilibrium dynamics is obtained in terms of the particlehole excitation. A single timedependent transition orbital is found to be largely responsible for the observed quantized pumping. Further, robustness of the nonadiabatic Thouless pumping is examined by introducing different types of chemical modifications. 
Thursday, March 17, 2022 2:18PM  2:30PM 
T46.00013: Lowenergy electron projectiles in water: Linear vs nonlinear energy loss Natalia E Koval, Fabiana Da Pieve, Bin Gu, Jorge Kohanoff, Emilio Artacho Lowenergy electrons as secondary projectiles are behind a significant part of the radiation damage affecting living matter. Research in the optimisation of ion radiotherapy and treatment of radiation poisoning in nuclearenergy environments or outer space make extensive use of Monte Carlobased cascade simulations (see e.g. [1]) using scattering cross sections and stopping power as input. The ones for electron stopping in liquid water are key input for those simulations. They are customarily obtained from linearresponse and phenomenology. Here we present first principles results for the quantum friction for lowenergy electron projectiles in water using timedependent densityfunctional calculations, both in linear response (frequency domain) and beyond linear, the latter based on explicit realtime simulations. The comparison reveals important deviations, nonlinear vs linear, around the Bragg peak, which might be significant for modelling. 
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