Ab initio determination of atomic structure and energy of surface states of bare and hydrogen covered GaN (0001) surface - Existence of the Surface States Stark Effect (SSSE)

► A stable structure of clean GaN(0001) surface posses (2×1) reconstruction, having every second row of Ga located near plane of N atoms. ► Ga-related dispersionless surface electronic state was obtained, already identified by angle resolved photoelectron spectroscopy. ► For the adsorbate density up to one H atom for each Ga surface atom, the adatoms are located at the on-top positions. ► The H-related quantum surface state is located at valence band maximum (VBM) and deeply in the valence band, about 2 eV below VBM for p- and n-GaN surface, respectively which is related to Surface States Stark Effect (SSSE).