SternheimerGW: A program for calculating GW quasiparticle band structures and spectral functions without unoccupied states

Abstract

The SternheimerGW software uses time-dependent density-functional perturbation theory to evaluate GW quasiparticle band structures and spectral functions for solids. Both the Green's function G and the screened Coulomb interaction W are obtained by solving linear Sternheimer equations, thus overcoming the need for a summation over unoccupied states. The code targets the calculation of accurate spectral properties by convoluting G and W using a full frequency integration. The linear response approach allows users to evaluate the spectral function at arbitrary electron wavevectors, which is particularly useful for indirect band gap semiconductors and for simulations of angle-resolved photoelectron spectra. The software is parallelized efficiently, integrates with version 6.3 of Quantum Espresso, and is continuously monitored for stability using a test farm. Program SummaryProgram Title: SternheimerGW Licensing provisions: GNU General Public License v3.0 Programming language: Fortran 2003 Nature of problem: The lack of the exchange-correlation discontinuity in density-functional theory (DFT) leads to a systematic underestimation of the band gap between conduction and valence states. Many-body perturbation theory in the GW approximation provides an effective solution to this problem, as well as other limitations faced by DFT in the description of electronic excitations. However, the GW method comes with its own set of limitations: (i) The perturbation of the system is typically expressed in terms of the unoccupied states, and achieving numerical convergence with respect to these states is often cumbersome. Since the underlying DFT codes rely only on the occupied states, their default behavior is often ill-suited to provide a sufficient amount of empty states. Combined with the large number of parameters that need to be converged, this limits the use of GW codes by non-expert users and automatic scripts. (ii) Currently, GW codes require that a homogeneous k-point * Corresponding authors.

QuasiparticleGWband structures and Fermi surfaces of bulk and monolayerNbS2

“…In the following, we will report the results of GW calculations for bulk and monolayer NbS 2 . These calculations have been performed at the G 0 W 0 level with the SternheimerGW code [56]. We recalculated the Fermi level using the G 0 W 0 quasiparticle eigenvalues to ensure the number of electrons is conserved [57].…”

The GW Compendium: A Practical Guide to Theoretical Photoemission Spectroscopy

“…To speed up Sternheimer G 0 W 0 , projection techniques for representing the dielectric matrix in an optimal, smaller basis (Wilson et al, 2008, 2009; Nguyen et al, 2012; Pham et al, 2013; Govoni and Galli, 2015) and Lanczos-chain algorithms that efficiently obtain the Sternheimer solution over a broad frequency range (Umari et al, 2010) have been developed. Furthermore, all the Sternheimer equations, that need to be solved for each r and ω, are independent from each other facilitating massively parallel implementation (Govoni and Galli, 2015; Schlipf et al, 2019).…”

Low-Order Scaling G0W0 by Pair Atomic Density Fitting

“… 46 , 54 , 56 , 57 The GW approximation makes MBPT computationally tractable, greatly improves over DFT for the description of single-particle excitations, 46 , 53 , 58 and also paves the way toward accurate optical spectra using the Bethe-Salpeter equation formalism. 59 , 60 Large numbers of computational material science codes 48 , 56 , 61 − 72 feature GW implementations, and also in the quantum chemistry community, it has acquired some momentum over the last years. 58 , 73 − 93 …”