  Permanent dipole moments of electronics states in non-centro-symmetric
materials play pivotal role in many phenomena. Correctly evaluating them
presents an arduous task and usually requires full knowledge of the band
structure as well as understanding the intricate concepts of Berry curvature.
Here we show that in a few cases (e.g. zinc blende and wurtzite) a rather
facile first-principle analytical derivation of the permanent dipole moments
using L Hopital rule can be performed, and the values and dispersion of these
dipoles near high symmetry points can be found using just a couple of widely
available material parameters. The results will hopefully contribute to better
understanding of shift currents, optical rectification and other
electro-optical phenomena.
