Based on a cluster model the adsorption of K on the graphite(0001)surface has been studied by using the charge self-consistent extended Hückel theory(EHT).The calculation is performed at four different coverages(Θ).The equilibrium adsorption heights obtained are in good agreement with experimental data and other theoretical values. The charge transfer Δ

Q

adsorption energy Δ

E

density of states(PDOS and TDOS)

Mulliken population and the bonding nature of the K/graphite systems are presented. It is worth noting that the Linear Muffin-tin Orbital(LMTO)method with the local functional theory has attained quite reliable results that are in qualitative agreement with those of the EHT.The results also show strong sensitivity of the electronic structure on the very little change of K-graphite layer spacing.This implies that K-graphite system is not a stable“single-phase”system.It is found that the K-4s and carbon-σ hybrid states are mainly situated in the lowest energy range discussed

which is the reason why K-4s states cannot be found at the Fermi level for K-graphite systems in the X-ray photoelectron spectroscopy(XPS)and angle-resolved ultraviolet photoelectron spectroscopy(ARUPS)measurements.The empty 3d-orbitals are believed to play a central role in present calculations with two different methods.