MODELING TRANSITION-METAL SURFACES WITH EMPIRICAL POTENTIALS

A study has been made of the surface energies and structures of Cu, Ag and Au, using two empirical potentials, namely the two- plus three-bo dy potential of Murrell and Mottram (MM) and the many-body potential o f Sutton and Chen (SC). The MM potential reproduces bulk properties mu ch better than SC (particularly in respect of the phonon dispersion cu rves), but for surface studies there are advantages and disadvantages to both. The many-body potential underestimates the average surface en ergies but gives the correct order of surface energies for different s urfaces. It correctly predicts a (1 X 2) reconstruction of the Au (110 ) surface. The two- plus three-body potential gives a much better matc h of the average surface energies of different surfaces, and the corre ct order of the unreconstructed surfaces. Two MM Au potentials have be en examined, one of which does not predict reconstruction of the (110) surface, whereas the other favours (1 X 3) over (1 X 2) reconstructio n. The SC potential gives consistently greater relaxation of the surfa ces than the MM potential. Some of the atomic displacements in this re construction are reproduced better with the MM potential than with the SC potential.