Structural and electronic properties of the (111)2×1 surface of Ge from first-principles calculations

We present results of a first-principles determination of the surface structure and electronic properties of Ge(111)2×{}1. We have found that the most stable state of this surface has a {π}-bonded chainlike structure. This structure has two different isomers with the tilt angle of the uppermost chains in opposite directions, and energetically very close to each other. The isomers exhibit a similar buckling of the surface chains, much larger that that of Si(111)2×{}1. They also show a very similar surface-state dispersion, which agrees well with the angle-resolved photoemission data of Nicholls et al.