Thermodynamical and structural properties of f.c.c. transition metals using a simple tight-binding model

Abstract

A semi-empirical model to simulate thermodynamic properties of f.c.c. transition metals is proposed. The attractive energy is derived within a second-moment approximation of the tight-binding scheme. The repulsive pairwise interaction is assumed to be of a Born-Mayer type and the parameters of the potential have been adjusted on the bulk modulus, the elastic constants and the cohesive energy. Bulk vibrational properties and defect energies for vacancies, interstitials and surfaces are estimated. Moreover, molecular dynamics simulations with this potential model to evaluate the high-temperature behaviour are presented. In particular, we have calculated the root-mean-square displacement and the thermal expansion as a function of temperature for Cu and Ni. These results allow us to test the anharmonicity of the potential. The agreement with experiment is quite good for low and intermediate temperatures. At high temperatures (T0·65Tm where T m is the melting temperature) the mean-square displacement increases too rapidly. Some possible origins of this discrepancy are discussed.