CALCULATED SURFACE ENERGIES OF THE 4D TRANSITION-METALS - A STUDY OF BOND-CUTTING MODELS

The surface energies of the low-index surfaces of the 4d transition metals were calculated using density-functional theory and the full-potential linear muffin-tin orbital method. The results are discussed in the context of bound-cutting models. It is found that the usual approach, which ignores the decrease of the bond strength with increasing coordination number, is incompatible with the calculated results. The coordination number - bond strength relation was calculated explicitly for several metals, showing that the bond strength decreases roughly as the reciprocal of the square-root of the coordination number. A modified model which takes this into account correctly describes the magnitude and the surface depencence of the calculated surface energies. In addition, we discuss the previously ignored role of the free-atom orbital structure in bond-cutting models.