Bond contraction in monolayers: 2d-hexagonal Cs

The first ab-initio all-electron theoretical/computational study of the energetics of a hexagonal Cs monolayer reveals that the CsCs nearest neighbor distance in the monolayer is reduced by about 11% compared with the corresponding distance in bulk Cs. This finding is in excellent agreement with measurements of the packing density of a hexagonal Cs overlayer on a W(110) surface. Model calculations show that this contraction is related to the formation of bands and the polarizability of the Cs 5p semi-core states.