Model description of transition metals using the rotated second moment approximation

Abstract

An interatomic potential is described, the rotated second moment approximation (RSMA), which incorporates directional bonding through energy moments evaluated over directional atomic orbitals. When non-directional orbitals are used, RSMA reduces to the standard SMA, and is thus capable of describing metallic systems. A model RSMA potential is demonstrated for 3d transition metals, with only first neighbor shell interactions, which can correctly predict the experimental trend in the relative stability of the fee and hep structures. A generalization of RSMA is proposed thai is related in the same way thai the embedded atom method (EAM) is related to the SMA. A generalized fee RSMA potential is constructed for which the Cauchy pressure can be made negative by systemaiically adjusting one parameier. This behavior results from the angular (directional) forces and not from a physically-unreasonable embedding function.