Electronic structure and phase transitions of submonolayer potassium on graphite

We study the electronic structure of K adlayers on graphite using a simplified tight-binding model in the coverage ({Θ}) range between 0.01 and 1.0 monolayers. We find that the coverage dependence of the K adsorption energy at low {Θ} arises mainly from the band-energy change reflecting the two-dimensional and semimetallic band structure of the substrate graphite rather than the dipole-dipole interaction. This former term is virtually absent for metallic substrates and thus may be the origin of the unusual structural properties observed recently in the K/graphite system.