Bulletin of the American Physical Society
APS March Meeting 2023
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session G61: Electrons, Phonons, ElectronPhonon Scattering and Phononics IVFocus

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Sponsoring Units: DCOMP Chair: Carla Verdi, University of Sydney Room: Room 418 
Tuesday, March 7, 2023 11:30AM  12:06PM 
G61.00001: Theory of nonlinear electronphonon coupling and its firstprinciples implementation Invited Speaker: Ion Errea Despite a huge effort has been devoted to develop first principles methods to calculate efficiently the impact of lattice quantum effects and anharmonicity on the structural, vibrational, and superconducting properties of materials, the electronphonon interaction is always calculated in the linear approximation, i.e., truncating the expansion of the electronic potential at first order. This approach is questionable, at least, whenever anharmonic effects on the vibrational properties are large, such as in superconducting hydrides and systems undergoing chargedensity wave or ferroelectric transitions. Here we present a novel nonperturbative theory for the electronphonon coupling that can be implemented from first principles. We apply the new theory to superconducting palladium hydrides and show that, remarkably, highorder nonlinear effects are comparable in magnitude to the standard linear term. Nonlinearity reveals crucial to explain the superconductivity as well as the inverse isotope effect in this system. Our new theory may have a large impact on the ab initio calculation of all properties related to the electronphonon interaction, e.g. superconductivity and electrical conductivity, in highly anharmonic systems. 
Tuesday, March 7, 2023 12:06PM  12:18PM 
G61.00002: Electronphonon Renormalization of the Band Gaps of Solids from Wannierlocalized Optimally Tuned Screened RangeSeparated Hybrid Functionals Stephen E Gant, Guy Ohad, Francesco Ricci, Maria Camarasa Gomez, Jonah B Haber, Leeor Kronik, Bartomeu Monserrat, Jeffrey B Neaton Density functional theory (DFT) calculations of thermal and zeropoint properties of solids due to electronphonon interactions are known to be sensitive to the choice of exchangecorrelation functional. Furthermore, the use of the GW approximation can improve results but at a significant increase in computational cost. Recently, we have demonstrated the Wannierlocalized optimally tuned screened rangeseparated hybrid (WOTSRSH) functional [1] can be used to compute the band gaps of a variety of solids to a high degree of accuracy. Here, we present the use of the WOTSRSH functional to calculate the phonon spectrum and bandgap renormalization of representative semiconductors and insulators and find it can reproduce the accuracy of higher order methods like GW at a reduced computational cost. 
Tuesday, March 7, 2023 12:18PM  12:30PM 
G61.00003: Nonuniform grids for Brillouin zone integration and interpolation Siyu Chen, Pascal T Salzbrenner, Bartomeu Monserrat We present two developments for the numerical integration over the Brillouin zone. First, we introduce a nonuniform grid, which we refer to as the Farey grid, that generalizes traditional regular grids. Second, we introduce symmetryadapted Voronoi tessellation, a general technique to assign weights to the points in an arbitrary grid. Combining these two developments, we propose a strategy to perform Brillouin zone integration and interpolation that provides a significant computational advantage compared to the usual approach based on regular grids. We demonstrate our methodology in the context of firstprinciples calculations with the study of Kohn anomalies in the phonon dispersions of graphene and MgB_{2}, and in the evaluation of the electronphonon driven renormalization of the band gaps of diamond and bismuthene. In both cases, we find large speedups, whether density functional perturbation theory or finite difference methods are used. Besides, our results of bismuthene reveal that it preserves a sizable topological band gap at room temperature. In summary, our method opens up an avenue for designing the most appropriate nonuniform grid for any given task, with the prospect of saving valuable computational time and allowing for new frontiers in computational condensed matter physics to be charted. 
Tuesday, March 7, 2023 12:30PM  12:42PM 
G61.00004: Anisotropic MigdalEliashberg analysis of superconductivity in layered LiMgB compounds Gyanu P Kafle, Charlsey Tomassetti, Igor I Mazin, Aleksey Kolmogorov, Elena R Margine LiB, a predicted compound analogous to the MgB_{2} superconductor, has been recently synthesized via cold compression and quenched to ambient pressure. We reinvestigate the superconducting properties of LiB and find that the electronphonon coupling anisotropy is as essential as in MgB_{2}. Using the anisotropic Eliashberg formalism, we predict a critical temperature (T_{c}) to be in the 3242 K range, three times higher than prior estimates based on isotropic calculations. We probe other LiMgB binary and ternary layered materials and find metastable phases with T_{c} close to or even 1020% above the record 39 K value in MgB_{2}. 
Tuesday, March 7, 2023 12:42PM  12:54PM 
G61.00005: Calculating TemperatureDependent Electronic Structure of Semiconductors using a Dynamic TightBinding Model Martin Schwade, Maximilian J Schilcher, David A Egger For theoretical calculations of largescale system sizes or longer timescale phenomena the computational costs of typical density functional theory can present a steep barrier, which motivates the development of alternative approaches. Here, we propose an extension of the tightbinding (TB) formalism which allows for the efficient calculation of temperaturedependent properties of semiconductors with little computational effort. Our TB approach employs hybridorbital basis functions and distancedependent matrix elements that are calculated by numerical integration of the respective orbitals. Our method is straightforward since the TB parameters are only optimized at 0 K, which still provides a transferable scheme for accurate calculations of the electronic structure of semiconductors at finite temperatures. Combining the dynamic TB method with molecular dynamics, we show that it can account for dynamic changes to the symmetry of the crystal that are due to, e.g., lattice distortions. 
Tuesday, March 7, 2023 12:54PM  1:06PM 
G61.00006: Efficient MigdalEliashberg calculations with Intermediate Representation basis using the EPW code Hitoshi Mori, Tianchun Wang, MingChun Jiang, Takuya Nomoto, Ryotaro Arita, Elena R Margine Recent attempts have been made to reduce the number of frequency points for the Matsubara Green’s functions in finitetemperature manybody calculations in order to reduce the computational cost. A method based on the intermediate Representation (IR) basis [1] has proven successful for computing the transition temperature within the MigdalEliashberg approach for several superconductors, such as Nb and H_{3}S [2,3]. However, the calculations performed in these studies have been limited to a kaveraged electronphonon interaction kernel. We have taken a step forward and implemented the IR basis method in the EPW code to solve the anisotropic fullbandwidth MigdalEliashberg equations [4]. This enables accurate and efficient calculations of the superconducting gap and critical temperature on ultradense electron k and phonon q grids. In this talk, we will discuss the implementation and show results of some representative systems obtained using the EPW code with the IR basis. 
Tuesday, March 7, 2023 1:06PM  1:18PM 
G61.00007: Differential Formalism of Power Series Correction for Single particle Electron Green's Function: Applications to 1D Holstein Chain. Bipul Pandey, Peter Littlewood Based on our previous work on selfconsistent power series correction formalism^{1} present for single particle green's function we present two ODE based formalisms of Power series correction that go beyond the cumulant approximation and are scalable and fast. The first differential formalism of the power series gives the exact results on the Holstein chain for a large range or electronboson coupling constant and is faster than the selfconsistent formalism. The second differential formalism is even faster but faces severe instability for the same problem when the boson energy scale is comparable or smaller than the band width. We discuss this instability and show that it stems from the assumption made on the nature of correction to simplify the correction form. We finally discuss its implication to selfconsistent cumulant expansion. 
Tuesday, March 7, 2023 1:18PM  1:30PM 
G61.00008: Efficient compression of firstprinciples electronphonon interactions Yao Luo, Jinsoo Park, Dhruv C Desai, Marco Bernardi Firstprinciples calculations of electronphonon (eph) interactions have advanced materials science and physics. Combined with Wannier interpolation of eph matrix elements, one can compute a wide range of eph physical effects in real materials, including phononlimited transport, band structure renormalization, and superconductivity. However, Wannier interpolation remains a trialanderror, materialspecific computational step that currently hinders workflow automation and bottlenecks efficiency. 
Tuesday, March 7, 2023 1:30PM  1:42PM 
G61.00009: Ab initio investigations of optical properties of MgS and CaS beyond the harmonic approximation. Maribel NúñezValdez, Artem Chmeruk Using firstprinciples calculations based on density functional theory (DFT), we study the infrared (IR) optical properties of MgS and CaS. Firstly, we assess the efficacy of the harmonic approximation in the modeling of their vibrational spectra. Secondly, by comparing our results to available experimental data [1], we show that a more accurate description of the IR optical properties requires the inclusion of anharmonic effects. A more precise determination of the dielectric constant of these binary sulfides could help in the effective computation of microscopic mechanisms correlated to their macroscopic radiative behavior. Our results could, on one hand, shed light on using more effectively MgS and CaS towards energy storage materials [2], and on the other hand, help in the interpretation of data collected by future missions to Mercury to study the planet's surface, which is hypothesized to have an abundance of volatiles such as sulfur [3]. 
Tuesday, March 7, 2023 1:42PM  1:54PM 
G61.00010: Anomalous pressure dependence of lattice dynamics in PbTe: a simulation study Ruihuan Cheng, Yue Chen Understanding the highpressure lattice dynamics is crucial to modulate the thermal transport in thermoelectric materials beyond ambient environment. Herein, using molecular dynamics simulations in combination with an accurate machinelearning potential, we find an anomalous nonmonotonic pressure dependence of the frequency of the transverse acoustic (TA) phonon in PbTe. The longitudinal acoustic (LA), longitudinal optical (LO) and transverse optical (TO) phonons harden as expected when pressure increases. The wellknown doublepeak feature of the TO mode in PbTe gradually vanishes when pressure is enhanced. The theoretical results are compared with available experimental data to verify our calculations. Moreover, we have also calculated the lattice thermal conductivity under pressure and revealed the phonon transport mechanism. 
Tuesday, March 7, 2023 1:54PM  2:06PM 
G61.00011: Efficient full relaxation of crystal structures with quasiharmonic approximation: Application to pyroelectricity of GaN and ZnO Ryota Masuki, Takuya Nomoto, Ryotaro Arita, Terumasa Tadano We develop an efficient calculation scheme of quasiharmonic approximation (QHA) which enables the simultaneous optimization of all the structural degrees of freedom, i.e., the shape of the unit cell and the internal coordinates. We employ the IFC renormalization [1], which efficiently calculates the harmonic phonon dispersion of updated crystal structures without additional expensive DFT calculations. 
Tuesday, March 7, 2023 2:06PM  2:18PM 
G61.00012: Anderson localization of phonons in multibranch massdisordered systems Wasim R Mondal, Yi Zhang, Tom Berlijn, N. S. Vidhyadhiraja, Hanna Terletska The Anderson localization (AL) of phonons in disordered media has been receiving increasing interest 
Tuesday, March 7, 2023 2:18PM  2:30PM 
G61.00013: Pair distribution function analysis of CoZr_{2}structure alloys John A Schneeloch, Despina A Louca, Yoshikazu Mizuguchi, Yuto Watanabe The intermetallic compounds AZr_{2} are a diverse array of materials with interesting properties. CoZr_{2}, for example, has a negative caxis thermal expansion, even though the caxis thermal expansion of the isostructural NiZr_{2} is positive. Furthermore, CoZr_{2} has an anomalous decrease in its unit cell volume on warming above ~400 K. The AZr_{2} materials are also platforms for highentropy alloys such as Co_{0.2}Ni_{0.1}Cu_{0.1}Rh_{0.3}Ir_{0.3}Zr_{2}, which can provide an opportunity to study superconductivity in the highdisorder regime. Characterization of the local structure would be helpful in understanding the properties of the AZr_{2} compounds. To that end, we have performed pair distribution function (PDF) analysis on neutron diffraction data taken on NOMAD at the Spallation Neutron Source. We measured four samples, including CoZr_{2} and variants with Co partially substituted by Cu, Cu/Rh, and Ni/Cu/Rh/Ir. Across all samples, our data show a consistent discrepancy in the local structure relative to the average structure of AZr_{2}. We discuss possible causes for this discrepancy, as well as the role that the additional elements have in modifying the thermal expansion behavior. 
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