Structure of the diamond (111) surface: Single-dangling-bond versus triple-dangling-bond face.

We present converged first-principles calculations for the atomic and electronic structure of diamond ~111! surfaces based on density-functional theory in the local-density approximation. Singleand triple-danglingbond surfaces with 131, 231, and (A33A3)R30° translational symmetry are studied by means of totalenergy minimizations. The ground-state geometries and electronic band structures are computed. In contrast to earlier work we find the p-bonded chains to be nearly undimerized and unbuckled in the 231 Pandey reconstruction. Consequently, the electronic band structure exhibits no optical gap. Other structures are higher in total energy (p-bonded molecule model, relaxed truncated-bulk structure! or represent only saddle points at the Born-Oppenheimer energy surface ~graphitelike surface, strongly dimerized chains!. Chain and trimer reconstructions at the triple-dangling-bond C~111! surface are very close in energy and domains of different reconstructions can compete. These structures may explain recent scanning tunneling microscopy findings on films grown by chemical vapor deposition. @S0163-1829~96!04519-5#