Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F20: Firstprinciples Modeling of Excitedstate Phenomena in Materials V: Timedependent Density Functional TheoryFocus

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Sponsoring Units: DCOMP Chair: Yuan Ping, University of California, Santa Cruz Room: BCEC 157A 
Tuesday, March 5, 2019 11:15AM  11:51AM 
F20.00001: Timedependent density functional perturbation theory (TDDFPT) with LiouvilleLanczos recursion chains for large systemsizes: dispersion of the conventional and acoustic surface plasmons of high Millerindex vicinal surfaces of gold. Effect of spinorbit coupling and of the surface geometry. Invited Speaker: Nathalie Vast

Tuesday, March 5, 2019 11:51AM  12:03PM 
F20.00002: Propagation of maximally localized Wannier functions in realtime TDDFT Dillon C. Yost, Yi Yao, Yosuke Kanai Realtime, timedependent density functional theory (RTTDDFT) has attracted much attention in recent years as an approach to study a variety of excited state phenomena ranging from optical excitations to electronic stopping. Many applications of RTTDDFT involve the inclusion of a timedependent applied electric field to perturb the system. In the length gauge representation, one can apply a scalar electric field to localized orbitals, such as maximally localized Wannier functions (MLWFs). We have implemented a method in the QB@LL planewave pseudopotential RTTDDFT code to transform the timedependent KohnSham (TDKS) states into MLWFs, allowing for simulations with timedependent electric fields and for the calculation of absorption spectra and nonlinear optical responses for both isolated and periodic systems. The propagation of MLWFs in RTTDDFT gives access to dynamic polarization and quantities such as the MLWF spread, allowing for detailed analysis of a wide range of excitation phenomena. 
Tuesday, March 5, 2019 12:03PM  12:15PM 
F20.00003: Maxwell+TDDFT multiscale simulation for optical response of nanomaterials Mitsuharu Uemoto, Kazuhiro Yabana We have been developing a novel multiscale simulation method which combines the timedependent density functional theory (TDDFT)based first principles electron dynamics and finitedifferencetimedomain (FDTD)based electromagnetic calculations. We apply this method to light propagation / scattering problem by semiconducting silicon nanoparticles and nanodimer structures with the length scale at a few hundred nanometer, which are often used as building block of optical devices. Under an irradiation of an intense femtosecond laser pulse (I > 10^{10} W/cm^{2}), carrier excitations by multiphoton processes take place due to the enhanced light field at the focalspot / hotspot. Thus, this method offers a useful tool to analyze optical nonlinearity at nanostructures in the first principles level. 
Tuesday, March 5, 2019 12:15PM  12:27PM 
F20.00004: Maxwell + FirstPrinciples TDDFTMD MultiScale Simulation and Application to Impulsive Stimulated Raman Scattering Spectroscopy Atsushi Yamada, Kazuhiro Yabana Nonlinear optics in solids includes complex physics arising from coupled nonlinear dynamics of light electromagnetic fields, electrons, and phonons. We have developed a novel multiscale simulation method to trace coupled dynamics of electromagnetic field inside the material in macroscopic scale and electrons and atoms in solid in microscopic scale, where the Maxwell equations are solved to describe propagation of the light while firstprinciples Ehrenfest molecular dynamics (MD) calculation is performed based on timedependent density functional theory (TDDFT), extending our previously developed multiscale method. 
Tuesday, March 5, 2019 12:27PM  12:39PM 
F20.00005: Microscopic and macroscopic MaxwellTDDFT descriptions for lightmatter interaction in thin materials Shunsuke Yamada, Masashi Noda, Katsuyuki Nobusada, Kazuhiro Yabana We present a comprehensive theoretical framework for interaction of an ultrashort light pulse with a thin material based on the timedependent density functional theory (TDDFT). We introduce a microscopic description solving the Maxwell equations for the light electromagnetic fields and the timedependent KohnSham equation for the electron dynamics simultaneously in the time domain on a common realspace grid. This scheme can simulate the lightmatter interaction in thin films irrespective of the film thickness and the light intensity. For two limiting cases of extremely thin and sufficiently thick films, we develop approximate schemes. For the former, a 2D macroscopic description is developed: 2D response functions are introduced for a weak field, while time evolution equation is derived for an intense field. For the latter, the 3D macroscopic description coincides with the ordinary electromagnetism with the 3D bulk response functions for a weak field, or the multiscale MaxwellTDDFT scheme for a strong field, which our group developed previously. In this talk, we show results for Si thin films and discuss the applicability of the microscopic and macroscopic descriptions. 
Tuesday, March 5, 2019 12:39PM  12:51PM 
F20.00006: Magnetic Exciations in TDDFT with GGA kernel Nisha Singh, Peter Elliott, Tashi Nautiyal, J. Kay Dewhurst, Sangeeta Sharma In ordered magnets of all forms (ferromagnets, antiferromagents, ferrimagnets, etc.) we encounter wave like excitations that propagate through the lattice of ordered spins. Correctly predicting these collective excitation modes is essential for understanding the thermodynamic properties of such materials. Theoretically, TDDFT within the linear regime, can successfully capture these low energy spin waves. However, it requires an approximation to the exchangecorrelation (XC) kernel, which encapsulates the electronelectron interactions of the manybody systems. Despite the plethora of approximations for the XC energy functional, only the ALDA kernel has been implemented and applied to study these magnetic excitations. In the work presented here we climb up the Jacob’s ladder of functionals and derive the XC kernel for GGA functionals. This is then tested by calculating the magnon spectra for simple ferromagnets and Heusler ferrimagnets using the PBE GGA functional. 
Tuesday, March 5, 2019 12:51PM  1:03PM 
F20.00007: Orbital magnetooptical response of periodic insulators from first principles David Strubbe, Irina Lebedeva, Ilya V. Tokatly, Angel Rubio We present a reformulation of density matrix perturbation theory for timedependent electromagnetic fields under periodic boundary conditions, which allows us to treat the orbital magnetooptical response of solids at the ab initio level. We use timedependent densityfunctional theory (TDDFT) with the Sternheimer equation, implemented in the Octopus realspace code, to solve for the gaugeinvariant part of the density matrix via the modern theory of polarization. Our computational scheme has an efficiency comparable to standard linearresponse calculations of absorption spectra. Calculations of magnetic circular dichroism spectra for adenine, cyclopropane, and bulk silicon agree with the available experimental data. A clear signature of the valley Zeeman effect is revealed in the magnetooptical spectrum of a single layer of hexagonal boron nitride, with a gfactor similar to that observed in monolayer transitionmetal dichalcogenides. The present formalism opens the path towards the study of magnetooptical effects in strongly driven lowdimensional systems. 
Tuesday, March 5, 2019 1:03PM  1:15PM 
F20.00008: A General Model Order Reduction Scheme for the Evaluation of Spectroscopic Properties and Excited States David WilliamsYoung, Roel Van Beeumen, Chao Yang, Xiaosong Li Due to the importance of spectroscopic methods in experimental physical chemistry, a primary directive in quantum chemistry is to be able to accurately and efficiently predict and interpret the response of molecular systems to external perturbations. Molecular response properties may be described in terns of propagators, such as the single particle Green's function and polarization propagator. Traditional methods to solve these problems, such as partial eigenvalue decompositions and direct linear system solves, become computationally intractable in cases where the spectral region of interest lies in the propagator's spectral interior. In this work is presented a novel model order reduction (MOR) technique for the rapid evaluation of molecular properties in arbitrary spectral regions. MOR accelerates the evaluation of these properties by constructing a rational Krylov subspace which spans the spectral region of interest. Numerical studies demonstrating the favorable computational cost and scaling of this method for linear response TDDFT are presented. Further, it will be demonstrated that bright eigenstates of the Hamiltonian may also be extracted from the same subspace. The proposed MOR algorithm will enable routine inquiry into previously intractable spectroscopic problems. 
Tuesday, March 5, 2019 1:15PM  1:27PM 
F20.00009: Truncated methods applied to the direct calculation of exciton binding energies. Aritz Leonardo, Mikel Arruabarrena, Aitor Bergara, Andres Ayuela Optical processes in insulators and semiconductors, including excitonic effects, can be described in principle exactly using timedependent densityfunctional theory (TDDFT). Within this formalism, a family of exchangecorrelation kernels known as longrangecorrected (LRC) kernels (fxc=α/q^{2}) have shown to accurately reproduce optical spectra for several insulators and semiconductors. More recently, Ullrich and coworkers adapted the Casida equation formalism suitable for determining molecular excitations to periodic solids, this way the exciton binding energy may be calculated in a direct way without having to compute explicitly the response function. However, it appears that no LRCtype kernel is capable of simultaneously produce good optical spectra and quantitatively accurate exciton binding energies. In the present work we have adapted Casida's formalism following a different approach. The long range nature of the kernel, i.e. the q→0 singularity, is regularized employing a supercell wignerseitz truncation that clearly alters the previously calculated alpha values of the kernel. We will justify our calculation method and provide the alpha values for several insulating/semiconducting materials. 
Tuesday, March 5, 2019 1:27PM  1:39PM 
F20.00010: Simulating valence and core excitons in solids within velocitygauge realtime TDDFT. Sri Chaitanya Das Pemmaraju The application of realtime TDDFT (RTTDDFT) to describe lightmatter interactions in periodic solidstate systems has thus far been largely limited to situations where excitonic effects are not crucial primarily due to the inability of semilocal exchangecorrelation (XC) functionals to describe exciton binding. In particular the simulation within TDDFT of accurate coreexcitation spectra that are often strongly modulated by solidstate excitonic effects has been hindered. In this work, a recent atomic orbital basis implementation [1] of realtime TDDFT that exploits rangeseparated hybrid XC functionals within the generalized KohnSham formulation [2] to simultaneously describe both valence and core excitonic effects in solids is presented. Optical properties and excitons in a number of representative solidstate systems are discussed from a timedomain perspective. Applications of the methodology to timeresolved core and valence spectroscopies are illustrated. 
Tuesday, March 5, 2019 1:39PM  1:51PM 
F20.00011: Relativistic realtime timedependent density functional theory for molecular properties Lukas Konecny, Marius Kadek, Kenneth Ruud, Michal Repisky We present the development and applications of relativistic realtime timedependent density functional theory. The method is based on the fourcomponent Dirac–Coulomb Hamiltonian in the basis of restricted kinetically balanced Gaussian functions exploiting the noncollinear Kramers unrestricted formalism. A quasirelativistic twocomponent X2C Hamiltonian obtained from the original fourcomponent Hamiltonian by an algebraic decoupling transformation is also considered. The equation of motion is formulated for the oneelectron density matrix and solved in a series of discrete time steps utilizing the second order Magnus propagator corrected by a selfconsistent extrapolationinterpolation procedure. Induced dipole moments recorded during simulations are transformed to the frequency domain to yield molecular spectra. Presented methodology includes scalar and spinorbit relativistic effects variationally. It is demonstrated for valence and core electron molecular spectroscopies such as electron absorption and circular dichroism. 
Tuesday, March 5, 2019 1:51PM  2:03PM 
F20.00012: ABSTRACT WITHDRAWN

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