Hubbard correlations and charge transfer at the GaAs(110) surface with alkali adsorbates

We have performed density-functional-theory (DFT) calculations for potassium adsorbed on GaAs(110). The results show that alkali adatoms mainly act as donors giving their electrons to Ga-derived surface states. We found that these states consist of well localized Ga dangling bonds, which allowed us to map the DFT results on a two-dimensional Hubbard model. To calculate the Hubbard U and the charge-transfer parameter {Δ} we simulate the electron transfer between adjacent orbitals. We find that U and {Δ} are of the same order as the hopping integral t, which brings the surface in the Mott-Hubbard regime.