On the stability of the W(001) surface

Recently, the present authors have suggested that some of the basic features of the unstable W(001)-(1×1) surface can be explained by the competition between the direct attractive and indirect repulsive interactions present at the surface. To understand this mechanism in more detail, number of surface structures (steps in the (0,1) and (1,1) direction, vacancy, adatoms etc.) have been investigated within a simple LCAO recursion scheme. The direct interactions (two-body term) and the indirect ones (three-body terms) are approximately additive for surface atoms and adatoms having four nearest neighbours. The unreconstructed (1×1) surface is under compressive (repulsive) stress and we suggest that, for example, steps should expand near their edges.