SIMPLE ANALYTICAL EMBEDDED-ATOM-POTENTIAL MODEL INCLUDING A LONG-RANGE FORCE FOR FCC METALS AND THEIR ALLOYS

A simple analytical embedded-atom method (EAM) model is developed. The model includes a long-range force. In this model, the electron-densit y function is taken as a decreasing exponential function, the two-body potential is defined as a function like a form given by Rose el nl. [ Phys. Rev. B 33, 7983 (1986)], and the embedding energy is assumed to be an universal form recently suggested by Banerjea and Smith. The emb edding energy has a positive curvature. The model is applied to seven fee metals (Al, Ag, Au, Cu, Ni, Pd, and Pt) and their binary alloys. A ll the considered properties, whether for pure metal systems or for al loy systems, are predicted to be satisfactory at least qualitatively. The model resolves the problems of Johnson's model for predicting the properties of the alloys involving metal Pd. However, more importantly , (i) by investigating the structure stability of seven fee metals usi ng the present model, we found that the stability energy is dominated by both the embedding energy and the pair potential for fcc-bce stabil ity while the pair potential dominates and is underestimated for fcc-h cp stability: and (ii) we find that the predicted total energy as a fu nction of lattice parameter is in good agreement with the equation of state of Rose et al. for all seven fee metals, and that this agreement is closely related to the electron density, i.e., the lower the contr ibution from atoms of the second-nearest neighbor to host density, the better the agreement becomes. We conclude the following: (i) for an E AM, where angle force is not considered, the long-range force is neces sary for a prediction of the structure stability; or (ii) the dependen ce of the electron density on angle should be considered so as to impr ove the structure-stability energy. The conclusions are valid for all EAM models where an angle force is not considered.