Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session J23: Theory and Simulation of Excited-State Phenomena in Semiconductors and Nanostructures II |
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Sponsoring Units: DCOMP Room: 202B |
Tuesday, March 3, 2015 2:30PM - 2:42PM |
J23.00001: Accurate effective masses from first principles Jonathan Laflamme Janssen, Xavier Gonze The accurate ab initio description of effective masses is of key interest in the design of materials with high mobility. However, up to now, they have been calculated using finite-difference estimation of density functional theory (DFT) electronic band curvatures. To eliminate the numerical noise inherent to finite-difference and obtain an approach that is more suitable for material design using high throughput computing, we develop a method allowing to obtain the curvature of DFT bands using Density-Functional Perturbation Theory (DFPT), taking a change of wavevector as a perturbation. Also, the inclusion of G$_0$W$_0$ corrections to DFT bands in our method will be presented. [Preview Abstract] |
Tuesday, March 3, 2015 2:42PM - 2:54PM |
J23.00002: Luttinger's approach to thermal transport in nanoscale conductors F.G. Eich, A. Principi, M. Di Ventra, G. Vignale The description of thermoelectric transport from first principles has recently attracted renewed interest due to its potential role in the development of sustainable energy sources. We will present our recent work [1] comparing Luttinger's approach [2] to thermal transport to the widely used Landauer-B\"uttiker formalism. We show that they coincide in the linear regime and highlight their differences in the nonlinear regime. Moreover, we discuss the asymptotic (steady state) and transient currents for a simple two-terminal setup. We will put these results in context with our recently proposed thermal Density-Functional Theory [3] and discuss strategies to define a local temperature.\\[4pt] [1] F. G. Eich, A. Principi, M. Di Ventra, and G. Vignale, Phys. Rev. B 90, 115116 (2014) \newline [2] J. M. Luttinger, Phys. Rev. 135, A1505 (1964) \newline [3] F. G. Eich, M. Di Ventra, and G. Vignale, Phys. Rev. Lett. 112, 196401 (2014) [Preview Abstract] |
Tuesday, March 3, 2015 2:54PM - 3:06PM |
J23.00003: Electronic and optical properties of a metal-organic framework with ab initio many-body perturbation theory Kristian Berland, Kyuho Lee, Sahar Sharifzadeh, Jeffrey B. Neaton With their unprecedented surface area, and their structural and chemical tunability, metal-organic frameworks (MOFs) are being thoroughly explored for applications related to gas storage. Less studied are their electronic, excited-state, and optical properties. Here we explored such properties of Mg-MOF-74 using a combination of density functional theory (DFT) and many-body perturbation theory (MBPT) within the GW approximation and the Bethe-Salpeter equation (BSE) approach. The near-gap electronic conduction states were found to fall into two distinct categories: molecular-like and 1d-dispersive. Further, using the BSE approach, we predict a strongly anisotropic absorption spectrum, which we link to the nature of its strongly-bound excitons. Our calculations are found to be in good agreement with experimental absorption spectra, validating our theoretical approach. [Preview Abstract] |
Tuesday, March 3, 2015 3:06PM - 3:18PM |
J23.00004: Polarization-dependent force driving the E$_\textrm{g}$ mode in bismuth under optical excitation: comparison of first-principles theory with ultra-fast x-ray experiments Stephen Fahy, Eamonn Murray Using first principles electronic structure methods, we calculate the induced force on the E$_\textrm{g}$ (zone centre transverse optical) phonon mode in bismuth immediately after absorption of a ultrafast pulse of polarized light. To compare the results with recent ultra-fast, time-resolved x-ray diffraction experiments [1], we include the decay of the force due to carrier scattering, as measured in optical Raman scattering experiments [2], and simulate the optical absorption process, depth-dependent atomic driving forces, and x-ray diffraction in the experimental geometry. We find excellent agreement between the theoretical predictions and the observed oscillations of the x-ray diffraction signal, indicating that first-principles theory of optical absorption is well suited to the calculation of initial atomic driving forces in photo-excited materials following ultrafast excitation. \\[4pt] [1] S. L. Johnson et al, Phys. Rev. B 87, 054301 (2013).\\[0pt] [2] J.J. Li et al, Phys. Rev. Lett. 110, 047401 (2013). [Preview Abstract] |
Tuesday, March 3, 2015 3:18PM - 3:30PM |
J23.00005: Nonadiabatic coupling and hot carrier relaxation in graphene quantum dots Jonathan Trinastic, Iek-Heng Chu, Hai-Ping Cheng Graphene quantum dots (GQDs) have many possible applications in a variety of research areas, including photovoltaics, catalysis, and sensors. Experimental research has suggested the existence of long hot carrier relaxation times on the order of 100-200 ps due to carrier-phonon interactions (Mueller et al 2011, \textit{Nano Lett, }\textbf{11}(1), 56-60), however little theoretical work has examined phonon-induced relaxation and its size or geometry dependence in these systems. We examine hot carrier relaxation due to lattice vibrations in GQDs of varying size and edge type (armchair or zigzag), using time-dependent density functional theory (TDDFT) to calculate nonadiabatic coupling between excitations. Employing the reduced density matrix method to calculate relaxation rates, we find a 100 ps relaxation time constant for low-lying excited states in a GQD with 132 carbon atoms, matching experiment. We also find that carbon-chain ligands attached to the GQD edges significantly change the nonadiabatic coupling and reduce nonradiative recombination rates to the ground state by an order of magnitude. GQDs with zigzag edges demonstrate a significantly longer hot carrier lifetime in low-lying excited states that approach the nanosecond time scale, suggesting the possibility of engineering a phonon bottleneck through geometry modification. [Preview Abstract] |
Tuesday, March 3, 2015 3:30PM - 3:42PM |
J23.00006: Excitons in solids with non-empirical hybrid time-dependent density-functional theory Carsten Ullrich, Zeng-hui Yang, Francesco Sottile The Bethe-Salpeter equation (BSE) accurately describes the optical properties of solids, but is computationally expensive. Time-dependent density-functional theory (TDDFT) is more efficient, but standard functionals do not produce excitons in extended systems. We present a new, non-empirical hybrid TDDFT approach whose computational cost is much less than BSE, while the accuracy for both bound excitons and the continuum spectra is comparable to that of the BSE. Good performance is observed for both small-gap semiconductors and large-gap insulators. [Preview Abstract] |
Tuesday, March 3, 2015 3:42PM - 3:54PM |
J23.00007: Electron Excitation Dynamics of Molecules Induced by Optical Near-Field Katsuyuki Nobusada, Masashi Noda Optical response of molecules is undoubtedly essential for understanding their physicochemical properties. In conventional theoretical approaches to the optical response, far-field light and matter interaction has been discussed. However, recent advanced nano fabrication allows us to produce very precise nanostructures and optical response in a nanometer region plays a crucial role in developing functional materials. To understand the nano-optical response, we must explicitly treat the light-matter interaction, i.e., optical near field and matter interaction, occurred in a nanometer region. Very recently, we have developed an original TDDFT computational method with the aim of understanding optical-near-field excitation dynamics in nanostructures. Our computed results clearly show interesting phenomena that are completely absent in the conventional optical response under a dipole approximation. We will discuss some computed results of unusual electron excitation dynamics such as two-photon excitation and dissociation of molecules by an optical near field. [Preview Abstract] |
Tuesday, March 3, 2015 3:54PM - 4:06PM |
J23.00008: First-principles calculation for electron dynamics in dielectrics induced by intense laser pulses Shunsuke A. Sato, Kazuhiro Yabana, Yasushi Shinohara, Kyung-Min Lee, Tomohito Otobe, George F. Bertsch We have been developing a theoretical and computational method to describe electron dynamics in crystalline solids irradiated by laser pulses. Our method is based on the time-dependent density functional theory (TDDFT), which enables us to treat quantum electron dynamics in the first principles level. By solving the time-dependent Kohn-Sham equation in real-time, it is possible to describe nonperturbative nonlinear electron dynamics induced by intense laser fields. We further combine the electron dynamics calculation in the TDDFT with the Maxwell's equation for electromagnetic fields so as to achieve simultaneous descriptions of both micro-meter-scale laser-field propagation and nanometer-scale electron dynamics induced by the fields. We call it ``Maxwell $+$ TDDFT multiscale simulation.'' As an application of the method, we show calculated transferred energy distribution from a laser pulse to a bulk SiO2 sample. We evaluated the laser damage threshold and the ablation depth from the distribution. We found that the calculation nicely reproduced measured results of both threshold and depth. [Preview Abstract] |
Tuesday, March 3, 2015 4:06PM - 4:18PM |
J23.00009: Study of attosecond dynamics of small and medium sized molecules induced by ultra-short optical pulses using TD-DFT Micael Oliveira, Gabriele D'Avino, Tomasz Kus, Benoit Mignolet, Theodoros Papadopoulos, Fran\c{c}oise Remacle, Matthieu Verstraete The advent of attosecond optical pulses, by allowing to control the breaking and rearrangement of chemical bonds, opens the door to many new applications, like novel catalysis mechanisms, photosensitive reactions, the preparation of states for quantum computing, etc. This control of the chemistry is made possible by the time scale of the attosecond pulses, which are effectively instantaneous with respect to the movement of the atomic nuclei, thus allowing the generation of a population of electronic states which is strongly out of equilibrium. In this work we investigate the electron dynamics of several molecular systems under the influence of attosecond pulses using the real-time formulation of time-dependent density functional theory (TD-DFT). We show a comparison of the performance of several exchange-correlation functionals by comparing TD-DFT calculations with equation of motion CCSD and CAS-SCF quantum chemistry methods, as well as applications of the method to the simulation of transient absorption spectroscopy. [Preview Abstract] |
Tuesday, March 3, 2015 4:18PM - 4:30PM |
J23.00010: Optical properties of alkali halide crystals from allĀ-electron hybrid-exchange TD-DFT calculations Ross Webster, Leonardo Bernasconi, Nicholas Harrison I will present a study of the electronic and optical properties of a series of alkali halide crystals, based on a recent implementation of(hybrid) TD-DFT in the all-electron Gaussian basis set code CRYSTAL [1]. This TD-DFT implementation includes on-site correlation and long range electron-hole interactions by including non-local Fock exchange in the functional. I will examine in particular, the impact of the Gaussian basis set size and quality on the prediction of the band gap, optical gap, and exciton binding energy of these systems, expanding on our previous work [2]. I will show that the polarisability criterion proposed by Rappoport and Furche for molecular systems [3], can be used to converge calculated excited-state properties with the basis set size for periodic systems. I will compare results from CRYSTAL calculations with GW+BSE calculations, previous plane-wave pseudopotential estimates and with experimental data. Finally, I will explore the potential for development of this method, including choice of exchange-correlation kernel, and our current work on a wide range of systems. \\[4pt] [1]: www.crystal.unito.it\\[0pt] [2]: L. Bernasconi et al., J. Phys.: Conf. Ser., 367, 012001 (2012)\\[0pt] [3]: D. Rappoport and F. Furche, J. Chem. Phys, 133, 134105 (2010) [Preview Abstract] |
Tuesday, March 3, 2015 4:30PM - 4:42PM |
J23.00011: A fast real time time-dependent density functional theory simulation method Lin-Wang Wang, Zhi Wang, Shu-Sheng Li We have developed an efficient real-time time-dependent density functional theory (TDDFT) method that can increase the effective time step from <1 attosecond in traditional methods to 0.1~0.5 femtosecond. Our algorithm, which carries out the non-adiabatic molecular dynamics TDDFT simulations, can have comparable speed to the Born-Oppenheimer (BO) ab initio molecular dynamics (MD). As an application, we simulated the process of an energetic Cl particle colliding onto a monolayer of MoSe2. Our simulations show a significant energy transfer from the kinetic energy of the Cl particle to the electronic energy of MoSe2, and the result of TDDFT is very different from that of BO MD simulations. This new algorithm will enable the use of real-time TD-DFT for many new simulations involving carrier dynamics and electron-phonon couplings. [Preview Abstract] |
Tuesday, March 3, 2015 4:42PM - 4:54PM |
J23.00012: Correlated Light-Matter Interactions in Cavity QED Johannes Flick, Camilla Pellegrini, Michael Ruggenthaler, Heiko Appel, Ilya Tokatly, Angel Rubio In the last decade, time-dependent density functional theory (TDDFT) has been successfully applied to a large variety of problems, such as calculations of absorption spectra, excitation energies, or dynamics in strong laser fields. Recently, we have generalized TDDFT to also describe electron-photon systems (QED-TDDFT) [1,2]. Here, matter and light are treated on an equal quantized footing. In this work, we present the first numerical calculations in the framework of QED-TDDFT. We show exact solutions for fully quantized prototype systems consisting of atoms or molecules placed in optical high-Q cavities and coupled to quantized electromagnetic modes. We focus on the electron-photon exchange-correlation (xc) contribution by calculating exact Kohn-Sham potentials using fixed-point inversions and present the performance of the first approximated xc-potential based on an optimized effective potential (OEP) approach.\\[4pt] [1] I. Tokatly, Phys. Rev. Lett. {\bf 110}, 233001 (2013).\\[0pt] [2] M. Ruggenthaler et.al., Phys. Rev. A {\bf 90}, 012508 (2014). [Preview Abstract] |
Tuesday, March 3, 2015 4:54PM - 5:06PM |
J23.00013: Fast Integral method for the calculation of Hartree and Exchange terms in DFT and TDDFT Michael Zuzovski, Amir Boag, Amir Natan The Hartree and Exchange terms can become a computational intensive task in DFT and TDDFT calculations of large structures. Existing methods use either iterative solvers such as conjugate gradient or multi-grid methods or use FFT for the calculation of those terms via the solution of the Poisson equation. With iterative solvers, the problem of setting the boundary conditions is often time consuming by itself as approximations such as the multipole expansion might not converge easily for structures with high aspect ratio. With FFT one needs to use a larger box for the calculation of finite systems. We present an alternative integral method to calculate the Hartree and Exchange terms in DFT and TDDFT. We first describe the algorithm and show that it has O(N) scaling for elongated structures. We then show some examples of long 1D chains ground state and time dependent calculations that use this algorithm. Finally we discuss some possible applications for more advanced functionals that include the Fock exchange or screened exchange. [Preview Abstract] |
Tuesday, March 3, 2015 5:06PM - 5:18PM |
J23.00014: Band Gap Studies in Density Functional Theory Thomas E. Baker, Lucas Wagner, Miles Stoudenmire, Kieron Burke, Steven White We examine the exact properties of Density Functional Theory (DFT) in one dimension and compare it with the numerically exact answer provided by Density Matrix Renormalization Group. Using the exact answers, we can compare exact Density Functional Theory quantities against commonly used approximations. Approximations tend to underestimate the band gap of the material. We compare the exact DFT quantities with the approximations to explore the band gap problem and provide numerical proofs of principle. [Preview Abstract] |
Tuesday, March 3, 2015 5:18PM - 5:30PM |
J23.00015: Real-time quantum electron-phonon dynamics Valerio Rizzi, Tchavdar Todorov, Jorge Kohanoff, Alfredo Correa Electrons and atomic motion out of equilibrium exchange energy and momentum. Physical problems that involve this exchange include Joule heating, inelastic electron tunneling, and thermalization of hot electrons in an irradiated material. An explicit dynamical treatment of both subsystems is essential to model such non-adiabatic phenomena and requires the ability to describe the interaction of the coupled electrons and nuclei without enforcing equilibration \textit{a priori}. Therefore, being able to describe an electronic system in real time together with the underlying ionic system is a key feature for first-principles electron-phonon methods. We have developed an approach for real-time phonon-assisted electron transfer in nanowires, explicitly tracking out-of-equilibrium systems that exchange energy. Our model is fully quantum mechanical: it overcomes the limitations of the Ehrenfest (quantum-classical) approximation and doesn't require thermostats, or the treatment of either subsystem as a bath. We can probe a range of timescales: from attoseconds (electronic timescale) to picoseconds (typical of atomic vibrations). The comparison with exact simulations of systems with a single phonon and a single electron have proved an invaluable validation tool for our method. We are able to describe the population inversion of an excited electronic system coupled to phonons and phonon-assisted conduction in systems with Anderson localization. [Preview Abstract] |
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