BerryPI: A software for studying polarization of crystalline solids with WIEN2k density functional all-electron package

We present a module that enables computation of polarization using density functional theory based on the full potential linearized augmented plane wave package WIEN2k. The theoretical background of deriving microscopic polarization of materials using the modern theory of polarization (geometric Berry phase approach) is reviewed. The software is validated and then applied to determine spontaneous polarization and Born effective charges of several crystal structures, which are commonly studied theoretically and experimentally.