Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session J18: Invited Session: Phonons and Electron-Phonon Interactions beyond LDA/GGA |
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Sponsoring Units: DCOMP Chair: David Vanderbilt, Rutgers University Room: Mission Room 103A |
Tuesday, March 3, 2015 2:30PM - 3:06PM |
J18.00001: Many-body effects on the zero-point phonon renormalization of the diamond band structure Invited Speaker: Michel C\^ot\' e The coupling of electrons to a bosonic field generally causes a renormalization of the energy levels. Whereas in vacuum, the electromagnetic fluctuations lead to the Lamb shift observed in the hydrogen atom levels, in condensed matter, the phonon field renormalizes the band structure, even at zero temperature. Being as large as several hundreds of meV, this renormalization is critical to the predictive power of ab initio calculations when it comes to absorption spectra, photovoltaic materials, or topological insulators. Following the early work of Fan and others in the 1950s, the problem was addressed by Allen, Heine and Cardona, whose theory provides perturbative expressions in terms of the electron-phonon coupling. Using semi-empirical methods, and later on, density functional theory (DFT), the temperature dependence of the band gap could be obtained for several semiconductors. Among those, diamond has become a case study where the zero-point renormalization is as much as half an election volt. The reliability of DFT for the electron-phonon coupling has however been challenged in recent years. Since the scattering of an electron by a phonon probes the excited states of a system, a theory describing this process should rely on an accurate unrenormalized band structure, unlike the one of DFT. A truly ab initio scheme however would rely on many-body perturbation theory. In this presentation, I will report on how a careful treatment using many-body perturbation theory as implemented by the GW approach result in an enhancement of the electron-electron interaction causing a 40\% enhancement in the zero-point renormalization (ZPR) in diamond with respect to the usual DFT treatment. [Preview Abstract] |
Tuesday, March 3, 2015 3:06PM - 3:42PM |
J18.00002: Radiative and nonradiative recombination at defects in semiconductors Invited Speaker: Audrius Alkauskas This talk will provide an overview of our recent work on the first-principles description of electron-phonon interactions at defects in semiconductors. Two aspects of this interaction have been addressed: (i) vibrational structure of defect luminescence bands [Phys. Rev. Lett. 109, 267401 (2012); New. J. Phys. 16, 073026 (2014)] and (ii) nonradiative carrier capture by means of multiphonon emission [Phys. Rev. B 90, 075202 (2014)]. The first process is related to the diagonal part, while the second one is related to the off-diagonal part of electron-phonon coupling. We show that in many situations it is necessary to go beyond traditional semilocal approximations to density functional theory not only to obtain a reliable description of defect geometries and charge-state transition levels, but also to accurately account for the interaction with the lattice during radiative or nonradiative processes. In particular, we demonstrate that hybrid density functionals yield luminescence lineshapes and nonradiative capture rates in very good agreement with experiment. Work performed in collaboration with Q. Yan, C. E. Dreyer, J. L. Lyons, and C. G. Van de Walle. [Preview Abstract] |
Tuesday, March 3, 2015 3:42PM - 4:18PM |
J18.00003: GW Many-Body Perturbation Theory for Electron-Phonon Coupling Calculations Invited Speaker: Carina Faber Within many-body perturbation theory (MBPT) and the GW approximation, we study the electron-phonon coupling (EPC) in carbon-based systems, taking as paradigmatic examples the fullerene molecule, graphene and diamond. It has been demonstrated by several groups that the strength of the electron-phonon coupling potential is in these cases significantly underestimated at the DFT-LDA level, while GW calculations offer an excellent agreement with experiments.\footnote{Faber, C., Laflamme-Janssen, J., C\^ot{\`e}, M., Runge, E. and Blase, X., Phys. Rev. B, 84, 155104 (2011)} \footnote{Lazzeri, M., Attaccalite, C., Wirtz, L. and Mauri, F., Phys. Rev. B, 78, 081406 (2008)} \footnote{Antonius, G., Ponc{\'e}, S., Boulanger, P., C\^ot{\`e}, M. and Gonze, X., Phys. Rev. Lett., 112, 215501 (2014)} Similar results have been obtained for superconducting bismuthates and transition-metal chloronitrides.\footnote{Yin, Z.P., Kutepov, A. and Kotliar, G., Phys. Rev. X, 3, 021011 (2013)} However, the related computational costs of evaluating the EPC strength at the GW level are high and thus represent strong limitations to a widespread application. We therefore discuss the accuracy of two less demanding alternatives on the MBPT level, namely the static Coulomb-hole plus screened-exchange (COHSEX) approximation and further the constant screening approach. In the latter, variations of the screened Coulomb potential W upon small changes of the atomic positions along the vibrational eigenmodes are neglected. We show that this latter approximation is most reliable, whereas the static COHSEX ansatz leads to substantial errors.\footnote{Faber, C., Boulanger, P., Attaccalite, C., Cannuccia, E., Duchemin, I., and Blase, X., submitted} These findings open the way for combining the present MBPT approach with efficient linear-response theories. [Preview Abstract] |
Tuesday, March 3, 2015 4:18PM - 4:54PM |
J18.00004: Electron-phonon coupling in organic semiconductors Invited Speaker: Jean-Luc Bredas |
Tuesday, March 3, 2015 4:54PM - 5:30PM |
J18.00005: Correlation-enhanced electron-phonon coupling Invited Speaker: Zhiping Yin Electron-phonon coupling (EPC) plays an important role in many material properties such as resistivity and conventional superconductivity. Accurate theoretical calculations of EPC in solids is essential for computational design, discovery and optimization of many functional materials. The widely used density functional theory (DFT) in the local density approximation (LDA) and generalized gradient approximation (GGA) can reasonably compute the EPC in weakly correlated materials but suffers from important shortcomings in strongly correlated materials. The self-energy of the quasiparticles in correlated materials modifies the LDA/GGA electronic structures hence the phonon frequencies and EPC. In this talk, I will discuss two types of underestimation of the EPC by LDA/GGA and propose a simple yet efficient methodology to evaluate the realistic EPC by using advanced electronic structure method beyond LDA/GGA. The extraordinarily high superconducting temperatures that are observed in two distinct classes of compounds--the bismuthates and the transition-metal chloronitrides can be readily accounted for by the correlation-enhanced EPC. Further impact of electronic correlation on the coupling of phonons and electronic degrees of freedom will also be discussed.\\[4pt] Reference: Z. P. Yin, A. Kutepov, and G. Kotliar, Phys. Rev. X 3, 021011 (2013). [Preview Abstract] |
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