Position of the Oxygen Overlayer on Al(111)

The energy bands, work function, Al $2p$ chemical shift, and oxygen binding energy have been calculated self-consistently for six-layer Al(111) films with oxygen overlayers at Z=0.55, 0.60, and 0.70 {} above the Al surface plane. Because the work function is extremely sensitive to Z, it has been estimated with very small uncertainty, Z=0.578±0.032 {}. This value is in excellent agreement with the values obtained from the chemical shift and binding energy as well as St\"ohr et al.'s experimental value.