An  ab initio  study was made of the (111) surface of -phase material in order to predict its structure, reconstruction and electronic state. Various structural possibilities were considered, and they were optimized by moving atoms according to Hellmann-Feynman forces. The results indicated that the unreconstructed surface was highly unstable, and that various reconstructions competed for the true ground state. Extrapolated trends, from diamond to Si to Ge, were well reproduced; with a 2 x 1 -bonded chain reconstruction prevailing in the absence of adatoms. In other cases, a c(4 x 2) or (2 x 2) basic adatom-restatom unit reconstruction prevailed. In both cases, the associated surface bucklings were larger than in Si and Ge; with consequently larger ionic charge transfer being predicted. A search for a -phase Sn-like metallic state of the surface was inconclusive.

Z.Y.Lu, G.L.Chiarotti, S.Scandolo, E.Tosatti: Physical Review B, 1996, 54[16], 11769-76