First-principles study of potassium adsorption on graphite

Theoretical results obtained with first-principles total-energy calculations are reported for potassium adsorption on the graphite (0001) surface. The structural parameters, the chemisorption energies, and the electronic properties of the K-graphite system are studied at two representative coverages, i.e., in the triangular (2×{}2) overlayer phase and at a lower coverage. The K-graphite bonding is characterized by a partial charge transfer from the adatom towards the substrate in the low-coverage regime, while in the (2×{}2) phase a lower charge transfer is accompanied by a redistribution of the electronic charge within the K overlayer. A very smooth surface characterizes the (2×{}2) K overlayer, which may help in explaining the exceedingly small diffracted intensities of He atoms from K-covered graphite recently reported. The unusual vibrational properties of the (2×{}2) overlayer are also studied and compared with recent experimental results.