Electrostatic energy and its contribution to elastic coefficients for body-centered-tetragonal metallic lattices

General expressions for the electrostatic energy and its contribution to the first- and second-order elastic coefficients are presented which can be used to evaluate the change in these quantities with arbitrary homogeneous deformations. Results are given for a bcc lattice under finite uniaxial deformation, i.e., the bct lattice. All the quantities calculated are shown to satisfy the internal check that the bct lattice with c/a=(2)1/2 is identical to the fcc lattice.