First-principles studies of water splitting at semiconductor and oxide surfaces Poul Georg Moses and Chris G. Van de Walle , Materials Department, University of California, Santa Barbara Electrostatic potential as a function of distance perpendicular to the surface. Plus signs mark atomic planes. A photoelectrochemical cell consists of a semiconductor photoelectrode which absorbs light in the solar spectrum with a valence-band maximum (VBM) and conduction-band minimum (CBM) that straddle the redox potential of water and hydrogen. We have investigated InGaN alloys using first-principles electronic-structure calculations and have determined the band gap and band positions as a function of In content. We find that up to 50% indium content the VBM and CBM indeed straddle the redox potential of water and hydrogen. Band positions as a function of In content