Model of metallic cohesion: The embedded-atom method

Abstract

The embedded-atom method (EAM) [Phys. Rev. B 29, 6443 (1984)] has proven to be a significant improvement in simplified total-energy calculations for metallic systems. In the current work, the ansatz used in the EAM is derived from the local-density functional for the energy. The expression demonstrated here is most appropriate for simple metals and for transition metals with nearly empty or nearly full d bands. An embedding energy is defined as a function of an optimal constant background density, and an equation for that optimal background density is obtained. The cohesive energy is then related to the embedding energy and an electrostatic two-body interaction. It is shown that lowest-order electronic relaxations can be absorbed into the same ansatz. Model calculations are presented for fcc nickel within the Thomas–Fermi–Dirac–von Weizsäcker model for the kinetic energy, with local exchange and correlation and frozen-electron distributions. The model is shown to provide a good description of the ground-state properties of nickel (e.g., energetics and structure of vacancies and surfaces) and also a good framework for evaluating the approximations used in justifying the EAM form. In particular, the model exhibits a simple relationship between the optimal constant background density and the background density at the atomic site. Corrections involving the gradient of the background density are shown to be important in the calculation of the surface energy. This work then provides a basis for the use of the EAM in semiempirical applications.