Multilayer relaxations and stresses on Mg surfaces

Using an ab initio approach based on density-functional theory in the local density approximation, nonlocal pseudopotentials and a plane-wave expansio n basis set, we show that trends in the relaxation patterns of the low-Mill er index surfaces of Mg can be traced to the nature of the Friedel oscillat ions in the surface charge densities. The oscillatory relaxation patterns t hat originate with contraction in the top interlayer spacing for Mg(10 (1) over bar 0) (14.9%) and Mg(11 (2) over bar 0) (5.0%) and expansion for Mg(0 001) (1.8%) are explained in a single consistent picture. We also find surf ace stress to be remarkably large along specific directions for Mg(10 (1) o ver bar 0) and Mg(11 (2) over bar 0). [S0163-1829 (99)06247-5].