Nonempirical cluster-model study of the chemisorption of atomic hydrogen on the (111) surface of diamondlike crystals

The interaction of atomic hydrogen with ${\mathrm{C}}_4$ ${\mathrm{H}}_9$, ${\mathrm{Si}}_4$ ${\mathrm{H}}_9$, and ${\mathrm{Ge}}_4$ ${\mathrm{H}}_9$ model clusters has been studied using all-electron and pseudopotential ab initio Hartree-Fock computations with basis sets of increasing flexibility. The results show that the effect of polarization functions is important in order to reproduce the experimental findings, but their inclusion only for the atoms directly involved in the chemisorption bond is usually sufficient. For the systems H-${\mathrm{C}}_4$ ${\mathrm{H}}_9$ and H-${\mathrm{Si}}_4$ ${\mathrm{H}}_9$ all-electron and pseudopotential results are in excellent agreement when basis sets of comparable quality are used. Besides, semiempirical modified-neglect-of-differential-overlap computations provide quite reliable results both for diamond and silicon and have been used to investigate larger model clusters. The results confirm the local nature of chemisorption and further justify the use of minimal $X_4$ ${\mathrm{H}}_9$ model clusters.