Dear Lei,
If your material is does not exhibit large electrostriction and piezoelectric effect , then you can ignore changes in lattice parameter. Other wise you need to generate multiple curves (energy vs. volume) each curve has a different c/a ration. Where c is the direction parallel to the field (typically elongated), and a is perpendicular to the field , typically shortened. Mostafa MIT
_______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum