Electronic State Unfolding for Plane Waves: Energy Bands, Fermi Surfaces, and Spectral Functions

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$_2$.