Theoretical calculations of H interacting with Si(100) 1 × 1

We have performed fully self-consistent calculations of the electronic properties of a monolayer of H interacting with a Si(100) 1 ×{} 1 surface in order to understand the chemisorptive properties of highly unsaturated Si surface atoms [Si (100) 1 ×{} 1 has two broken bonds per surface atom]. A total of eight separate geometries were studied, corresponding to Si-H separations ranging from 2.8 to 4.4 a.u. It was found that the Si monolayer had an equilibrium separation of 2.86 a.u. and an equilibrium force constant of $k=0.156$ a.u. The interaction potential between the H monolayer and the Si substrate was well fit by empirical interaction potentials of the Morse and Rydberg form, which implied a dissociation energy for the Si-H bond of 3.4 eV. The surface spectrum was also studied, the most interesting features of which were a Si-H bonding surface-state band similar in position to that found on Si(111), and a lone-orbital surface-state band, half occupied and essentially identical to the bridge bond state on clean Si(100).