P-rich GaP(001) (2x1)/(2x2) surface: A hydrogen-adsorbate structure determined from first-principles calculations

We perform first-principles total-energy and electronic structure calculations in order to determine the atomic structure of the P-rich (2 X 1)/(2 X 2) reconstruction commonly observed for GaP(001) surfaces grown by gas-phase epitaxy. A monolayer of buckled phosphorus dimers stabilized by hydrogen adsorbed in an alternating sequence is found to be energetically stable and to be consistent with the experimental data.