Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H58: FirstPrinciples Modeling of Electron Transport in MaterialsInvited

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Sponsoring Units: DCOMP DCMP Chair: Hartwin Peelaers, University of California, Santa Barbara Room: LACC Petree Hall C 
Tuesday, March 6, 2018 2:30PM  3:06PM 
H58.00001: Boltzmann Transport Theory for Thermoelectric Compounds Invited Speaker: David Singh Thermoelectrics are used for the conversion of thermal and electrical energy. They offer a number of advantages over competing technologies including scalability to small sizes and temperature differences, simple reliable designs and often low cost. However, these devices have not seen wide application in energy applications due to their limited conversion efficiency. This is a consequence of the limited performance of current thermoelectric materials, which can be characterized by a dimensionless figure of merit, ZT=σS^{2}T/κ. There is no known fundamental limit on ZT. However, the combination of transport parameters entering ZT is a contradictory combination that does not occur in ordinary materials. As revealed by Boltzmann transport calculations, electronic structure plays a remarkably subtle role in thermoelectric performance that can however be simply visualized in terms of isoenergy surfaces. A long sought connection is drawn between topological insulators and high ZT thermoelectrics, explaining the overlap between these two interesting materials classes. Characteristics that can be used to identify new thermoelectric compositions are discussed and an efficient computational screening method based on an electronic fitness function is presented. 
Tuesday, March 6, 2018 3:06PM  3:42PM 
H58.00002: ElectronPhonon Interaction in 2D ChargeDensityWave Materials Invited Speaker: Amy Liu Metallic layered transition metal dicalchogenides often exhibit multiple types of electronic ordering tendencies, such as charge density waves, superconductivity, and Mott insulator phases. The ability to vary the dimensionality of these materials from layered bulk samples to fewlayer and singlelayer materials has provided new opportunities to explore the interplay between electronphonon coupling, electron correlation, and interlayer interactions, which drive the ordering tendencies. Here we present firstprinciples calculations investigating how the electronphonon interaction depends on dimensionality, doping, and strain in several of these materials, and discuss the impact on charge density wave instabilities. 
Tuesday, March 6, 2018 3:42PM  4:18PM 
H58.00003: Predictive ab initio calculations of phononlimited carrier mobilities in semiconductors Invited Speaker: Feliciano Giustino One of the fundamental properties of semiconductors is their ability to support electric currents in the presence of electric fields (drift) or carrier concentration gradients (diffusion). These properties are described by transport coefficients such as electron and hole mobilities and diffusion coefficients. During the past decade there has been considerable progress in firstprinciples calculations of carrier transport starting from density functional theory, however the accuracy, reliability, and predictive power of current approaches are not fully established. Within this broad context, I will discuss our recent work on ab initio calculations of carrier mobilities in semiconductors. I will review the formalism leading to the Boltzmann transport equation, and discuss the key approximations underlying this approach. I will describe our implementation of the Boltzmann formalism within the electronphonon software package EPW [1], and discuss the computational challenges associated with the evaluation of the scattering integrals, the singular behavior of Fröhlich polar electronphonon coupling at long wavelengths [2,3], and the necessity to include manybody quasiparticle corrections to the electron band structures. I will illustrate these concepts using our recent calculations on wellknown semiconductors such as silicon, as well as new systems such as halide perovskites. I will conclude the talk by discussing the outstanding challenges in this area, and by pointing out promising avenues for future research [4]. 
Tuesday, March 6, 2018 4:18PM  4:54PM 
H58.00004: Conditions for T^{2} resistivity from electronelectron scattering Invited Speaker: Michael Swift Recent experiments in SrTiO_{3} and other materials have observed a scattering mechanism for which resistivity (ρ) is proportional to the square of the temperature (T). By analogy to a similar phenomenon observed in metals at low temperature, this mechanism was hypothesized to be Fermiliquidlike electronelectron scattering (Baber scattering), although it persists to much higher temperatures than Baber scattering in metals. To study this phenomenon, we employ a variational solution of the Boltzmann Transport Equation to solve the electronelectron collision integral directly, going beyond the relaxationtime approximation [1]. We show that the Baber T^{2} power law rests on several crucial assumptions. When these assumptions hold, ρ_{elel} is proportional to T^{2} (as we verified using our methodology in sodium metal). However, in the case of SrTiO_{3}, the assumptions do not hold, and we found that ρ_{elel} is no longer proportional to T^{2}. The higher the temperature and the lower the doping level, the greater the deviation from T^{2}. This suggests that the power law observed in SrTiO_{3} may instead be due to another, as yet unidentified, mechanism. More generally, this implies that observation of ρ proportional to T^{2} in a given system is not evidence for electronelectron scattering unless the assumptions behind the Baber T^{2} hold in that system. 
Tuesday, March 6, 2018 4:54PM  5:30PM 
H58.00005: Advances in Computing Charge Transport and Hot Carrier Dynamics from First Principles Invited Speaker: Marco Bernardi Calculations of transport and ultrafast dynamics of charge carriers have relied on heuristic approaches for the past several decades. Recent progress in combining density functional theory and related methods with kinetic equations, such as the Boltzmann transport equation (BTE), are enabling spectacular advances in computing carrier dynamics in materials from first principles. A special role is played by the interaction between charge carriers and lattice vibrations, also known as the electronphonon (eph) interaction, which dominates carrier dynamics near room temperature and for carrier energies within a few eV of the band edges in semiconductors. We will discuss methods we recently developed that advance the understanding of carrier dynamics in materials, including: 
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