  Ion displacements are the cause of the ferroelectricity in perovskites. By
properly shifting ions, ab initio computations have been extensively used to
investigate properties of perovsites in various structural phases. In addition
to the relatively simple ion displacements, perovskites have another type of
structural distortion known as antiferrodistortion or oxygen octahedron
tilting. The interplay between these two types of distortions have generated
abundant structural phases that can be tedious to prepare for ab initio
computation, especially for large supercells. Here, we design and implement a
computer program to facilitate the generation of distorted perovskite
structures, which can be readily used for ab initio computation to gain further
insight into the perovskite of a given structural phase.
