Contribution of strain to the valence EFG in a cubic metal

Unlike the earlier works, which evaluated the electrostatic potential V and its derivatives at the un-relaxed position of the host ions, we have evaluated them at the relaxed position. Besides improving consistency, this approach allows one to study the direct influence of lattice relaxation and strain on V, V_ij and hence on the valence electric field gradient q^v. For the nearest neighbours in Al host, this effect is shown to change q^v by up to 18%.