Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H7: First-Principles Modeling of Excited-State Phenomena III: TDDFTFocus
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Sponsoring Units: DCOMP DCP DMP Chair: Andre Schleife, University of Illinois at Urbana-Champaign Room: 266 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H7.00001: Excitons in solids with time-dependent density-functional theory: the long-range corrected kernel and beyond Young-Moo Byun, Carsten Ullrich Time-dependent density-functional theory (TDDFT) can describe the optical properties of solids in principle more efficiently than the Bethe-Salpeter equation, but the construction of good approximations to the exchange-correlation (xc) kernel is challenging. Since the long-range ($ -1/q^2 $) behavior is a key for producing bound excitons in solids, many long-range corrected (LRC) xc kernels have been proposed, among them the so-called "bootstrap" kernel. However, closely related LRC-type kernels have been reported in the literature to yield conflicting results. Here, we reveal the origin of the confusion, present a new choice-free LRC kernel which yields exciton binding energies of semiconductors and insulators accurately and efficiently, and discuss the general limitations of LRC-type xc kernels. This work was supported by NSF Grant DMR-1408904 [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H7.00002: Transient Spectra in TDDFT: Corrections and Correlations John Parkhill, Triet Nguyen We introduce an atomistic, all-electron, black-box electronic structure code to simulate transient absorption (TA) spectra and apply it to simulate pyrazole and a GFP chromophore derivative\footnote{T. Nguyen J. Koh and J. Parkhill Journal of Physical Chemistry Letters, 2016}. The method is an application of OSCF2, our dissipative extension of time-dependent density functional theory. We compare our simulated spectra directly with recent ultra-fast spectroscopic experiments, showing that they are usefully predicted. We also relate bleaches in the TA signal to Fermi-blocking which would be missed in a simplified model. An important ingredient in the method is the stationary-TDDFT correction scheme recently put forwards by Fischer, Govind, and Cramer which allows us to overcome a limitation of adiabatic TDDFT. We demonstrate that OSCF2 is able to predict both the energies of bleaches and induced absorptions, as well as the decay of the transient spectrum, with only the molecular structure as input. With remaining time we will discuss corrections which resolve the non-resonant behavior of driven TDDFT, and correlated corrections to mean-field dynamics. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H7.00003: Theoretical design of near - infrared organic compounds. Katarzyna Brymora, Laurent Ducasse, Olivier Dautel, Christine Lartigau-Dagron, Frédéric Castet The world follows the path of digital development faster than ever before. In consequence, the Human Machine Interfaces (HMI) market is growing as well and it requires some innovations. The goal of our work is to achieve an organic Infra-Red (IR) photodetectors hitting the performance requirements for HMI applications. The quantum chemical calculations are used to guide the synthesis and technology development. In this work, in the framework of density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we consider a large variety of materials exploring small donor-acceptor-donor molecules and copolymers alternating donor and acceptor monomers. We provide a structure-property relationship in view of designing new Near-Infrared (NIR) absorbing organic molecules and polymers. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:42PM |
H7.00004: Application of non-adiabatic electron dynamics to non-linear response and electrical conductivity of materials Invited Speaker: Alfredo A. Correa Real-time Time dependent density functional theory gives us access to detailed evolution of quantum electronic system, both in the linear and the non-linear regime. As the power and scale of TDDFT computer simulations grows, new phenomena can be captured and studied by this technique. In this talk, we present a new method and simulation results regarding materials undergoing particle radiation and its relationship to the optical response and conductivity. We obtain that there is a minimum of the DC-electrical conductivity as a function of current in a disordered metallic system and present a model that can explain these simulation results. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H7.00005: TDDFT excitations in polymer density-functional first-principles calculations John Mintmire Over the past several years we have made substantial progress in developing an approach for density-functional electronic structure calculations on quasi-one-dimensional nanostructures with helical periodic symmetry. This approach calculates a first-principles total energy and band structure using an all-electron Gaussian-basis set. In this talk we discuss the application of a Casida-equation scheme to calculate excitation energies and excited states in such nanostructures within a time-dependent density-functional theory (TDDFT) approach. We present some preliminary results for carbon nanotubes and graphitic nanoribbons where we examine localization trends in the excited states. This research was supported in part by an appointment to the Higher Education Research Experience for Faculty sabbatical program at Oak Ridge National Laboratory program. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H7.00006: Maxwell+TDDFT multiscale method for light propagation in thin-film semiconductor Mitsuharu Uemoto, Kazuhiro Yabana First-principles time-dependent density functional theory (TDDFT) has been a powerful tool to describe light-matter interactions and widely used to describe electronic excitations and linear and nonlinear optical properties of molecules and solids. We have been developing a novel multiscale modeling to describe a propagation of light pulse in a macroscopic medium combining TDDFT and Maxwell equations. In the method, the finite-difference time-domain (FDTD)-like electromagnetism (EM) calculation is carried out in a macroscopic grid. At each grid point, the time-dependent Kohn-Sham equation is solved in real time. In the presentation, we show applications of this method to the 1D/2D propagations of femtosecond laser pulses through a thin-film semiconductor. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H7.00007: Examining Physical and Numerical Approximations in Real-Time TDDFT Non-Equilibrium Dynamics Simulations for Determining Electronic Stopping Power Dillon C. Yost, Yi Yao, Yosuke Kanai The accurate prediction of electronic stopping power, the rate of energy transfer from swift ions to electrons in matter, is of great importance in developing future technologies in areas such as nuclear energy, space electronics, and thermal neutron detection. In recent years, real-time time-dependent density functional theory (RT-TDDFT) has been employed to calculate electronic stopping power from first principles. While the predictions from these first-principles non-equilibrium simulations agree very well with experimental data for ion velocities below the so-called Bragg peak of the electronic stopping power curve, in all cases there remains a significant underestimation of experimental results beyond the Bragg peak. In this work, we thoroughly inspect the details of RT-TDDFT electronic stopping simulations by examining various physical and numerical approximations employed in practical calculations. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H7.00008: Non-adiabatic approximations and exact conditions in TDDFT Johanna I. Fuks, Soeren E. B. Nielsen, Neepa T. Maitra Almost all calculations today in time-dependent Density Functional Theory (TDDFT) utilize an adiabatic approximation for the exchange-correlation potential, however it is known that non-adiabatic features of the exact potential can have a large impact on the dynamics, especially when a system is driven far from its ground state. In this work, we explore the development of non-adiabatic functional approximations based on the decomposition of the exact exchange-correlation potential in terms of an interaction component and a kinetic component [J. Chem. Phys. 140, 18A515 (2014)]. In particular, we investigate different approximations to these two components in the light of the fulfilment of the following exact conditions: zero force theorem, harmonic potential theorem, memory condition and constant resonances condition. We study several cases of non-equilibrium dynamics and correlate poor performance with the violation of one or more of these exact conditions. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H7.00009: Time-dependent density-functional approach for exciton binding energies Aritz Leonardo, Aitor Bergara Optical processes in insulators and semiconductors, including excitonic effects, can be described in principle exactly using time-dependent density-functional theory (TDDFT). Ullrich and co-workers adapted the Casida equation formalism for molecular excitations to periodic solids, which allows to obtain in a direct way, exciton binding energies without having to evaluate the response function. However, in this type of calculations the problem always arises from the lack of proper long-range behavior of the exchange correlation kernels in general. From a computational point of view, the kernels that exhibit Coulomb like tails need a special attention in periodic solids. More recently, Sundararaman and Arias developed an original and efficient method based on the Minimum Image Convention (MIC) in which Coulomb type interactions are truncated on Wigner-Seitz super-cells for the calculation of exchange energies of periodic solids. We have implemented this numerical scheme for the direct calculation of exciton binding energies of various small- and large-gap semiconductors, as the earlier mentioned Casida formalism resembles Fock type exchange integrals. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H7.00010: Using the particle-hole map to analyze charge transfer excitations in molecular complexes Edward A Pluhar, Yonghui Li, Carsten A Ullrich The particle-hole map (PHM) is a computational tool to visualize electronic excitations (calculated using time-dependent density-functional theory), based on representations in canonic molecular orbital transition space. We have effectively demonstrated the PHM’s ability to map out the origins and destinations of electrons and holes and, hence, the roles of different functional units of organic molecules during an excitation. Beyond the standard canonical representation, transformation to localized orbitals is a common technique. We analyze the PHM as a visualization tool for both canonical and localized molecular orbital representations in various inorganic and organic charge-transfer complexes. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H7.00011: Insights of the Ultrafast Charge Transfer Process in CdSe Quantum Dot/Organic Molecule System: A Real-Time Time-Dependent Ab Initio Study. Zhi Wang, Jan-Philip Merkl, Mona Rafipoor, Holger Lange, Lin-Wang Wang, Gabriel Bester We report for the first time a real-time time-dependent density function theory (rt-TDDFT) simulation on experimental size CdSe quantum dot/organic molecule system, to analyze its ultrafast (femtosecond to sub-picosecond) photoexcited charge transfer (CT) dynamics. Non-adiabatic dynamic details, such as the size-dependence of CT process, the carrier separation and cooling, the electron-phonon interaction and Auger-assisted process are presented using our high-efficient rt-TDDFT package. Our results are in excellent agreement with experiment data. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H7.00012: Ab initio evidence for nonthermal characteristics in ultrafast laser melting Chao Lian, Shengbai Zhang, Sheng Meng Laser melting of semiconductors has been observed for almost forty years; surprisingly, it is not well understood where most theoretical simulations show a laser-induced thermal process. Ab initio nonadiabatic simulations based on real-time time-dependent density functional theory reveals for the first time intrinsic nonthermal melting of silicon, at a temperature far below thermal melting temperature of 1680~K. Both excitation threshold and time evolution of diffraction intensity agree well with experiment. Nonthermal melting is attributed to excitation-induced drastic changes in bonding electron density, and subsequent decrease in melting barrier, rather than lattice heating as previously assumed in the two-temperature models. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H7.00013: Simulating Excitons in MoS2 with Time-Dependent Density Functional Theory Cedric Flamant, Grigory Kolesov, Efthimios Kaxiras Monolayer molybdenum disulfide, owing to its graphene-like two-dimensional geometry whilst still having a finite bandgap, is a material of great interest in condensed matter physics and for potential application in electronic devices. In particular, MoS2 exhibits significant excitonic effects, a desirable quality for fundamental many-body research. Time-dependent density functional theory (TD-DFT) allows us to simulate dynamical effects as well as temperature-based effects in a natural way given the direct treatment of the time evolution of the system. We present a TD-DFT study of monolayer MoS2 exciton dynamics, examining various qualitative and quantitative predictions in pure samples and in the presence of defects. In particular, we generate an absorption spectrum through simulated pulse excitation for comparison to experiment and also analyze the response of the exciton in an external electric field.In this work we also discuss the electronic structure of the exciton in MoS2 with and without vacancies. [Preview Abstract] |
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