Two-band second moment model and an interatomic potential for caesium

A semiempirical formalism is presented for deriving interatomic potentials for materials such as caesium or cerium which exhibit volume collapse phase transitions. It is based on the Finnis-Sinclair second-moment tight-binding approach, but incorporates two independent bands on each atom. The potential is cast in a form suitable for large-scale molecular dynamics, the computational cost being the evaluation of short-ranged pair potentials. Parameters for a model potential for caesium are derived and tested.