Ab initio plane-wave pseudopotential density functional theory (DFT) calculations have been carried out to determine the atomic and electronic structure of the $\mathrm{K}∕\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}R{30}^{\mathrm{°}}\text{−}B$ adsorption system at $1∕3$ monolayer coverage. Chemisorption of the potassium atoms has been found to leave the topology and bonding structure of the $\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}R{30}^{\mathrm{°}}\text{−}B$ substrate essentially unchanged. The results also show that the lowest-energy $\mathrm{K}∕\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}R{30}^{\mathrm{°}}\text{−}B$ structures are very similar to the most energetically favorable geometries for the $\mathrm{K}∕\mathrm{Si}\left(111\right)7\times 7$ chemisorption system. The minimum energy configuration has been found to be a structure in which the potassium atoms are positioned near the hollow $H_3$ sites, the boron atoms occupy the subsurface $S_5$ positions, and the silicon adatoms are located at the $T_4$ sites. The electronic structure of this lowest-energy $\mathrm{K}∕\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}R{30}^{\mathrm{°}}\text{−}B$ configuration has been found to be metallic.

• Received 17 November 2003

DOI:https://doi.org/10.1103/PhysRevB.70.235325