  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$_2$.
