Electronic state unfolding for plane waves: energy bands, Fermi surfaces and spectral functions

TL;DR

This paper introduces an efficient unfolding scheme integrated into VASP that simplifies the analysis of electronic structures in complex materials by mapping supercell calculations to primitive cell Brillouin zones, enabling easier interpretation of energy bands, Fermi surfaces, and spectral functions.

Contribution

The paper presents a novel, resource-efficient unfolding method embedded in VASP that automates the reconstruction of electronic band structures from supercell calculations.

Findings

Successfully applied to doped BaFe2(1-x)Ru2xAs2 superconductor

Analyzed adsorbate interactions and polaronic states on TiO2(110)

Investigated band splitting due to spin fluctuations in EuCd2As2

Abstract

Modern computing facilities grant access to first-principles density-functional theory study of complex physical and chemical phenomena in materials, that require large supercell to properly model the system. However, supercells are associated to small Brillouin zones in the reciprocal space, leading to folded electronic eigenstates that make the analysis and interpretation extremely challenging. Various techniques have been proposed and developed in order to reconstruct the electronic band structures of super cells, unfolded into the reciprocal space of an ideal primitive cell. Here, we propose an efficient unfolding scheme embedded directly in the Vienna Ab-initio Simulation Package (VASP), that requires modest computational resources and allows for an automatized mapping from the reciprocal space of the supercell to primitive cell Brillouin zone. This algorithm can computes band structures, Fermi surfaces and spectral functions, by using an integrated post-processing tool (bands4vasp). The method is here applied to a selected variety of complex physical situations: the effect of doping on the band dispersion in the BaFe$_{\rm 2(1-x)}$Ru$_{\rm 2x}$As$_2$ superconductor, the interaction between adsorbates and polaronic states on the TiO$_2$(110) surface, and the band splitting induced by non-collinear spin fluctuations in EuCd$_2$As$_2$.