3 BODY FORCES IN THE LATTICE-DYNAMICS OF FCC METALS

There are presently experimental data on FCC metals, concerning fundamentally harmonic properties (dispersion curves, second order elastic constants) and essentially anharmonic ones (third order elastic constants, thermal expansion). However, at present, there is not a simple interatomic potential that can reproduce adequately all this experimental information simultaneously. In this work we develop several programs to calculate the second order elastic constants and the dispersion curves using a general central two body interaction up to 19th neighbors and common nearest neighbor three body interactions. The difference from previous works is that here the three body potential is a purely angular one, uncoupled from the two body forces, allowing a quantitative evaluation of its relative importance.