Energy dependence of exact muffin-tin-orbital structure constants

We investigate the energy dependence of the exact muffin-tin-orbital slope matrix in the complex energy plane. Analytic expressions for the asymptotic behavior of the slope matrix and its first energy derivative for large imaginary energies are given. We demonstrate that a two-center Taylor type expansion of the slope matrix accurately reproduces the exact values within a complex energy range covering the usual energy window used in electronic structure calculations. As an application, we study the composition dependence of the lattice parameters of the MgY binary system, a candidate material for hydrogen storage applications.