Piezoelectric Effect

The piezoelectric effect is a phenomenon exhibited by certain crystals of expansion in one direction (axis) and contraction in another direction, as the result of an applied electric field.  Also, an applied mechanical strain in one direction causes electric charges of opposite signs to appear on different faces of the crystal.  This phenomenon can be modeled by simply altering the different translation vectors of a solid.  That is, altering the Tv bond-length from the optimized value would simulate stress in that direction. After geometry optimization, with the Tv bond length not optimized, the change in electric charges from the values for the relaxed crystal would be a measure of the piezoelectric effect..

This type of phenomenon might be easier to model using Cartesian coordinates.