Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J27: Focus Session: Computer Simulations of Interactions of Electromagnetic Fields and Nanostructures |
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Sponsoring Units: DCOMP Chair: Kalman Varga, Vanderbilt University Room: 501 |
Tuesday, March 4, 2014 2:30PM - 3:06PM |
J27.00001: First-Principles Description of Strong Electromagnetic Fields in Solids Invited Speaker: Kazuhiro Yabana Interactions between light and matter are usually described by two theories: Macroscopic Maxwell equations describe propagation of a light in a medium, while quantum calculation of susceptibilities such as dielectric function is one of central issues in the first-principles calculation. Recent progresses of laser technologies, however, require theories beyond it. Strong electromagnetic fields of a laser pulse induce extremely nonlinear electron dynamics which no more allows perturbative separation between macroscopic electromagnetic fields and microscopic electron dynamics. We have recently developed a multi-scale theory for this problem, describing electron dynamics in solid using real-time time-dependent density functional theory. This theory provides a quite general and computationally feasible basis for the problem, including ordinary macroscopic electromagnetism in a weak field limit and being applicable to problems involving arbitrarily intense fields. In my presentation, I will discuss the basic theory, computational implementation, and physics applications of our new approach. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J27.00002: First Principles Real-Space GW+BSE Calculations for Confined Systems Linda Hung, Serdar Ogut, Jaime Souto, Alex Lee, Charles Lena, James R. Chelikowsky, Felipe H. Da Jornada, Steven G. Louie We investigate the performance of various levels of GW theories for electronic excitations as well as the resulting solutions of the Bethe-Salpeter-Equation (BSE) for optical excitations in a wide range of confined systems including atoms, ions, diatomic molecules, and organic molecules relevant for photovoltaic applications. Starting with solutions of the Kohn-Sham equations for ground state properties computed via the real-space {\em ab initio} pseudopotential code PARSEC, we perform the GW calculations in the space of single-particle transitions at various levels of theory, and compare the results with photoemission data. The levels of theory include such approximations as $G_0W_0$ with RPA screening, $G_0W_f$ that includes vertex corrections through the use of a dielectric screening within the time-dependent-local-density approximation (TDLDA), the $GW_0$, and the self-consistent GW. The resulting quasiparticle energies and wave functions from the GW calculations are used to solve the BSE for optical excitations, which are then compared with experiments and results from calculations performed within the TDLDA. The effects of the vertex corrections, self-consistency in GW, and core-valence partitioning are discussed. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J27.00003: Kadanoff-Baym-Keldysh-Ehrenfest dynamics of correlated materials responding to ultrafast laser pulses Lazar Kish, Roland Allen In our many earlier simulations of the response of materials and molecules to laser pulses, one-electron states were determined by the time-dependent Schr\"{o}dinger equation with an instantaneous one-electron Hamiltonian. These states were then used with Ehrenfest's theorem in a semiclassical treatment of the coupled dynamics of electrons and nuclear coordinates. For strongly-correlated materials, however, true nonequilibrium self-energies are required. Here we describe a practical numerical procedure for employing the Kadanoff-Baym/Keldysh equations together with Ehrenfest's theorem. In preliminary work we treat the simplest possible model of a system in which there is the potential for both a Peierls structural transition (involving doubling of the unit cell) and a Mott-Hubbard electronic transition (involving electron correlations). These calculations are relevant to understanding the dynamics of insulator-metal phase transitions in VO$_{2}$, which has been studied in ultrafast pump-probe measurements [1-3] and nanoscale imaging [4]. \\[4pt] [1] C. K\"{u}bler, Phys. Rev. Lett. 99, 116401 (2007).\\[0pt] [2] M. van Veenendaal, Phys. Rev. (in press).\\[0pt] [3] A. Cavalleri et al., Phys. Rev. B 70, 161102(R) (2004).\\[0pt] [4] M. M. Qazilbash et al., Phys. Rev. B 83, 165108 (2011). [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J27.00004: Effective transient states for nonequilibrium systems under ultrafast control pulses Bin Hwang, Jenni Portman, Edward Ersoy, Phillip Duxbury We investigate the transient states in nonequilibruim time-dependent systems. Intense ultrafast laser pulses allow the preparation of transient states of matter exhibiting strong non-equilibrium between electrons and lattice. By controling the laser pulse, we are able to change the transient states of these quantum systems. The optical and structural properties as well as the temporal evolution of such states provide insight into the mutual dependence of electronic and atomic structure. We approach the problem by showing examples from charge-density-wave systems and model two level systems. In both of these, nonequilibrium techniques can be used to qualitatively describe the common short-time experimental features. Through simulations based on non-equilibrium Green's function formalism and time dependent master equations approaches we show how to achieve effective transient states for nonequilibrium systems under ultrafast control pulses. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 4:18PM |
J27.00005: Dynamics of irradiation: from molecules to nano-objects and from material science to biology Invited Speaker: Eric Suraud We discuss microscopic mechanisms of irradiation in clusters and molecules. We consider the case of isolated molecules/clusters [1] possibly in contact with an environment [2]. We use Time Dependent Density Functional Theory (for electrons) coupled to Molecular Dynamics (for ions) and follow explicitly in time both irradiation and response of the system. Examples are taken from free metal clusters, from fullerenes, from molecules of biological interest and from clusters deposited on a surface or embedded in a matrix [3,4]. We analyse in particular the properties of emitted electrons (photo electron spectra, angular distributions\textellipsis ), which constitute a key tool of analysis of the properties of irradiated clusters and molecules [5]. We also discuss the possibility of pump and probe scenarios (opening the road to manipulation at the molecular scale) with help of dedicated laser pulses, exploring high laser frequencies towards the FEL regime and very short times scales down towards the attosecond domain.\\[4pt] [1] F. Calvayrac et al, Phys. Reports (2000)4932\\[0pt] [2] P. M. Dinh et al, Phys. Reports (2009) 433\\[0pt] [3] Z.P. Wang et al, Int. J. Mass Spect. (2009) 14304\\[0pt] [4] U. F. NdongmuoTaffoti et al, Eur. Phys. J. D (2010) 1315\\[0pt] [4] Th. Fennel et al, Rev. Mod. Phys. (2010) 1793. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J27.00006: The time-dependent particle-hole map: one-dimensional benchmark studies Yonghui Li, Carsten Ullrich The time-dependent particle-hole map (TD-PHM) is a computational tool for visualization and interpretation of electronic excitation processes in many-body systems, in particular for molecular systems that are used in organic photovoltaics. In practice, the TD-PHM is obtained from time-dependent Kohn-Sham calculations, which implies three types of approximations: approximation to the exchange-correlation (xc) potential, replacement of exact many-body wave function with the corresponding Kohn-Sham Slater determinant, and, for molecules, the reduction of the six-dimensional TD-PHM to a 2-dimensional object suitable for representation in real space. Here, we focus on the first two approximations, and study one-dimensional lattice systems with several electrons interacting via soft-Coulomb potentials. We carry out benchmark calculations and to assess the validity of approximate xc potentials and the replacement of the exact wave functions with Kohn-Sham Slater determinants. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J27.00007: Time-dependent density functional theory of magneto-optical response of periodic insulators Angel Rubio, Ilya V. Tokatly, Irina V. Lebedeva Though the linear response theory has been successfully used for molecular systems for a long time, the extension of this theory to solids is not straightforward since the position operator is ill defined in extended periodic systems. The theoretical description of homogeneous static magnetic field in periodic systems is particularly challenging as the corresponding vector potential breaks the translational invariance of the Hamiltonian. We present a unified approach to calculation of all-order response to arbitrary electromagnetic fields both for periodic and molecular systems within the formalism of non-equilibrium Green functions. The approach is applied to derive the expression for the magneto-optical response of insulating solids in the approximation of non-interacting electrons. The formula obtained is completely identical to the expression for molecular systems if the proper position and orbital magnetization operators are chosen. The terms corresponding to changes in the optical response due to the orbital magnetization of Bloch states and due to the modified density of Bloch states in the magnetic field are identified. A computational scheme based on the density matrix-perturbation theory is developed for practical calculations of the magneto-optical response. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J27.00008: \emph{Ab initio} study of optical excitations in VO$_2$ John Coulter, Adam Gali, Efstratios Manousakis Motivated by recent experimental efforts to fabricate p-n junctions from transition metal oxides (TMOs) and a recent theoretical study claiming TMOs to be good absorbers and promising materials for efficient carrier multiplication, we study the optical properties of a prototypical TMO, the insulator $M_1$ phase of vanadium dioxide (VO$_2$), by \emph{ab initio} methods. We applied the Bethe-Salpeter equations (BSE) to calculate the optical properties, starting from self-consistent GW quasi-particle energy levels and states. In contrast to expectations, the exciton binding energy obtained by BSE is in good agreement with the experiment. We find that the electron-electron interaction is very strong which makes this material promising for efficient carrier multiplication that might lead to an enhanced efficiency in photo-voltaics applications. To illustrate this more quantitatively, we calculated the impact ionization rate within the independent quasiparticle approximation, and find that the rate is significantly higher than silicon in the region of highest solar intensity, due to the strong multiple carrier excitations. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J27.00009: Nanoscope based on nanowaveguides A.H. Rose, B. Wirth, R.E. Hatem, A.P. Rashed Ahmed, M.J. Burns, M.J. Naughton, K. Kempa The far field spatial resolution of conventional optical lenses is of the order of the wavelength of light due to loss in the far field of evanescent, near electromagnetic field components. We show that subwavelength details can be restored in the far field with an array of divergent nanowaveguides, which map the discretized, subwavelength image of an object into a magnified image observable with a conventional optical microscope. We demonstrate that metallic nanowires, nanocoaxes, and nanogrooves can be used as such nanowaveguides. Thus, an optical microscope capable of subwavength resolution --- a nanoscope --- can be produced, with possible applications in a variety of fields where nanoscale imaging is of value, including living systems. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J27.00010: The Anderson-Condon-Shortley Site in X-ray Spectroscopies of Solids Bernard Delley, Anne-Christine Uldry Electronic structures of compounds involving open d- and f- shell are studied frequently by X-ray and electron spectroscopies. The excitation, especially core excitation, is localized on a single site makes this the problem of impurity site states interacting with the continuum of bands. on the other hande, the electron-electron interaction whithin the d- or f- shell leads to a multiplet problem as addressed long ago for isolated atoms. Building on our easy to use program multiX (*), which treats an atom in a general crystal field environment without symmetry analysis, we now address the interaction of this atomic entity with the band continuum. The crossover from atomic to bandlike spectra is the focus of interest. We discuss experimental examples where available and accessible to our methods. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J27.00011: Opto-electronic properties of silicon nanoparticles: Excitation energies, sum rules, and Tamm-Dancoff approximation Marton Voros, Dario Rocca, Adam Gali, Giulia Galli We present an ab initio study of the excited state properties of silicon nanoparticles (NPs) with diameters of 1.2 and 1.6 nm. Quasiparticle corrections were computed within the GW approximation. The absorption spectra were computed by time-dependent density functional theory (TDDFT) using the adiabatic PBE approximation, and by solving the Bethe-Salpeter equation (BSE). In our calculations we used recently developed accelerated methods that avoid the explicit inversion of the dielectric matrix and summations over empty states [1]. We found that the scissor approximation reliably describes quasiparticle corrections for states in the low energy part of the spectra. We also found good agreement between the structure and positions of the absorption peaks obtained using TDDFT and the BSE. We discuss the effect of the Tamm-Dancoff approximation on the optical properties of the NPs and present a quantitative analysis in terms of sum rules. In the case of the BSE we found that, even in the absence of the Tamm-Dancoff approximation, the f-sum rule is not fully satisfied due to the inconsistency between the approximations used for the BSE kernel and for the quasiparticle Hamiltonian. [1] D. Rocca, D. Lu,G. Galli, J. Chem. Phys. 133, 164109 (2010). [Preview Abstract] |
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