Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F20: First-principles Modeling of Excited-state Phenomena in Materials V: Time-dependent 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: Time-dependent density functional perturbation theory (TDDFPT) with Liouville-Lanczos recursion chains for large system-sizes: dispersion of the conventional and acoustic surface plasmons of high Miller-index vicinal surfaces of gold. Effect of spin-orbit coupling and of the surface geometry. Invited Speaker: Nathalie Vast
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Tuesday, March 5, 2019 11:51AM - 12:03PM |
F20.00002: Propagation of maximally localized Wannier functions in real-time TDDFT Dillon C. Yost, Yi Yao, Yosuke Kanai Real-time, time-dependent density functional theory (RT-TDDFT) 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 RT-TDDFT involve the inclusion of a time-dependent 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 plane-wave pseudopotential RT-TDDFT code to transform the time-dependent Kohn-Sham (TDKS) states into MLWFs, allowing for simulations with time-dependent electric fields and for the calculation of absorption spectra and nonlinear optical responses for both isolated and periodic systems. The propagation of MLWFs in RT-TDDFT 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 time-dependent density functional theory (TDDFT)-based first principles electron dynamics and finite-difference-time-domain (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 > 1010 W/cm2), 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 + First-Principles TDDFT-MD Multi-Scale 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 multi-scale 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 first-principles Ehrenfest molecular dynamics (MD) calculation is performed based on time-dependent density functional theory (TDDFT), extending our previously developed multi-scale method. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F20.00005: Microscopic and macroscopic Maxwell-TDDFT descriptions for light-matter 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 time-dependent density functional theory (TDDFT). We introduce a microscopic description solving the Maxwell equations for the light electromagnetic fields and the time-dependent Kohn-Sham equation for the electron dynamics simultaneously in the time domain on a common real-space grid. This scheme can simulate the light-matter 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 Maxwell-TDDFT 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 exchange-correlation (XC) kernel, which encapsulates the electron-electron interactions of the many-body 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 magneto-optical 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 time-dependent electromagnetic fields under periodic boundary conditions, which allows us to treat the orbital magneto-optical response of solids at the ab initio level. We use time-dependent density-functional theory (TDDFT) with the Sternheimer equation, implemented in the Octopus real-space code, to solve for the gauge-invariant part of the density matrix via the modern theory of polarization. Our computational scheme has an efficiency comparable to standard linear-response 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 magneto-optical spectrum of a single layer of hexagonal boron nitride, with a g-factor similar to that observed in monolayer transition-metal dichalcogenides. The present formalism opens the path towards the study of magneto-optical effects in strongly driven low-dimensional 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 Williams-Young, 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 time-dependent density-functional theory (TDDFT). Within this formalism, a family of exchange-correlation kernels known as long-range-corrected (LRC) kernels (fxc=-α/q2) have shown to accurately reproduce optical spectra for several insulators and semiconductors. More recently, Ullrich and co-workers 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 LRC-type 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 super-cell wigner-seitz 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/semi-conducting materials. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F20.00010: Simulating valence and core excitons in solids within velocity-gauge real-time TDDFT. Sri Chaitanya Das Pemmaraju The application of real-time TDDFT (RT-TDDFT) to describe light-matter interactions in periodic solid-state systems has thus far been largely limited to situations where excitonic effects are not crucial primarily due to the inability of semi-local exchange-correlation (XC) functionals to describe exciton binding. In particular the simulation within TDDFT of accurate core-excitation spectra that are often strongly modulated by solid-state excitonic effects has been hindered. In this work, a recent atomic orbital basis implementation [1] of real-time TDDFT that exploits range-separated hybrid XC functionals within the generalized Kohn-Sham formulation [2] to simultaneously describe both valence and core excitonic effects in solids is presented. Optical properties and excitons in a number of representative solid-state systems are discussed from a time-domain perspective. Applications of the methodology to time-resolved core and valence spectroscopies are illustrated. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F20.00011: Relativistic real-time time-dependent density functional theory for molecular properties Lukas Konecny, Marius Kadek, Kenneth Ruud, Michal Repisky We present the development and applications of relativistic real-time time-dependent density functional theory. The method is based on the four-component Dirac–Coulomb Hamiltonian in the basis of restricted kinetically balanced Gaussian functions exploiting the noncollinear Kramers unrestricted formalism. A quasirelativistic two-component X2C Hamiltonian obtained from the original four-component Hamiltonian by an algebraic decoupling transformation is also considered. The equation of motion is formulated for the one-electron density matrix and solved in a series of discrete time steps utilizing the second order Magnus propagator corrected by a self-consistent extrapolation-interpolation procedure. Induced dipole moments recorded during simulations are transformed to the frequency domain to yield molecular spectra. Presented methodology includes scalar and spin-orbit 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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