  Structural stability and electronic properties of alkaline-earth metals (Ca,
Sr, Ba) induced Si(111)-3x2 surfaces have been comprehensively studied by means
of ab initio calculations. Adsorption energy and charge density difference
calculations show the high structural stability due to the strong chemical
bonding. Analysis of electronic band structures and band-decomposed charge
density distributions indicates that the third valence band is deriving from
top Si and metal atoms, while the top most two valence bands are deriving from
the bulk silicon. These results suggest a larger surface band gap of 1.65-1.68
eV, which is good consistent with the recent experimental finding for
Sr/Si(111)-3x2 surface. These results reveal a natural explanation for the
relevant experimental observation and stimulate further experimental and
theoretical exploration on the surface science.
