Ab Initio Electron-Phonon Interactions in Correlated Electron Systems

Abstract

Electron-phonon (e-ph) interactions are pervasive in condensed matter, governing phenomena such as transport, superconductivity, charge-density waves, polarons, and metal-insulator transitions. Firstprinciples approaches enable accurate calculations of e-ph interactions in a wide range of solids. However, they remain an open challenge in correlated electron systems (CES), where density functional theory often fails to describe the ground state. Therefore reliable e-ph calculations remain out of reach for many transition metal oxides, high-temperature superconductors, Mott insulators, planetary materials, and multiferroics. Here we show first-principles calculations of e-ph interactions in CES, using the framework of Hubbard-corrected density functional theory (DFT þ U) and its linear response extension (DFPT þ U), which can describe the electronic structure and lattice dynamics of many CES. We showcase the accuracy of this approach for a prototypical Mott system, CoO, carrying out a detailed investigation of its e-ph interactions and electron spectral functions. While standard DFPT gives unphysically divergent and shortranged e-ph interactions, DFPT þ U is shown to remove the divergences and properly account for the longrange Fröhlich interaction, allowing us to model polaron effects in a Mott insulator. Our work establishes a broadly applicable and affordable approach for quantitative studies of e-ph interactions in CES, a novel theoretical tool to interpret experiments in this broad class of materials.

Superconductivity in black phosphorus and the role of dynamical screening

“…For the phononic part, an improved starting point could be obtained from a DFT+DMFT calculation of the phonons, 56,57 or using DFT+U . 58,59 To summarize, our results show that many-body calculations of the screened interaction W in combination with the parameter-free SCDFT framework for calculating T c provides a framework which is capable of predicting the correct range of T c values in the simple cubic phase of black phosphorus. While the frequency dependence of the interaction is important for obtaining realistic T c values, it is not solely responsible for the peculiar pressure versus T c dependence that has been observed in experiments.…”

HP -- A code for the calculation of Hubbard parameters using density-functional perturbation theory

“…[10]. In fact, by constructing the localized perturbation (typically requiring costly calculations in supercells) as a series of independent monochromatic perturbations in the primitive unit cell, it improves significantly the computational efficiency, accuracy, user-friendliness, and automation [2,3], as also demonstrated by several recent applications [14,41,15,42,43,44,45,46,47,48,49]. Key to this successful implementation of the LR-cDFT is indeed the capability to express perturbation theory in reciprocal space as in the calculation of phonons using DFPT [50,51,52].…”

Electron correlations rule phonon-driven instability in single layer TiSe$_2$

“…To simulate phonon dynamics while properly accounting for electron correlations, we utilize density functional perturbation theory (DFPT) [53,54] corrected with onsite Coulomb (Hubbard) interaction U [55][56][57] (see Supplemental Material (SM) [58] for more computational details), which was proven to be affordable and accurate tool for quantitative studies of EPC in correlated materials [59].…”