Development of simple SPD tight-binding models for transition metals

A simple spd tight-binding scheme for atomistic simulations in transition metals is developed using an orthogonal basis set in the two-center approximation. The purpose of the present approach is to cope with the limitations of the canonical d-band model for elements at the beginning or at the end of the transition metal series while keeping a reduced number of parameters, and simple decay-functions. The parameters for the hopping integrals are fitted to FP-LMTO calculations of the volume dependence of band energies and band structures for several selected structures. Constant values are taken for the on-site energies, and the Born-Mayer pair potential is used for the repulsive term. Two approaches are compared for the total energy: the band model and the bond model. First applications are presented in the case of zirconium, where the difference between these models on phase stability results is particularly drastic. The bond model reproduces the stability of the hcp phase and displays a good agreement with experiments for the elastic constants.