Born charges
Add code to calculate Born charges using wannier functions and finite displacements.
The born effective charge of an atom in a structure quantifies how the polarization of the structure changes upon the displacement of the atom:
Omega dP_i
Z_aij = ----- * -----
e dR_aj
Polarization can be calculated using localized Wannier functions, where the electronic contribution is directly proportional to the sum of the occupied Wannier centers. Finally, the derivative is evaluated by calculating a simple central difference based on finite displacements in each of the coordinate directions.