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-functi onal theory in the local-density approximation. Single- and triple-dan gling-bond surfaces with 1X1, 2X1, and (root 3X root 3)R30 degrees tra nslational symmetry are studied by means of total-energy minimizations . The ground-state geometries and electronic band structures are compu ted. In contrast to earlier work we find the pi-bonded chains to be ne arly undimerized and unbuckled in the 2X1 Pandey reconstruction. Conse quently, the electronic band structure exhibits no optical gap. Other structures are higher in total energy (pi-bonded molecule model, relax ed truncated-bulk structure) or represent only saddle points at the Bo rn-Oppenheimer energy surface (graphitelike surface, strongly dimerize d chains). Chain and trimer reconstructions at the triple-dangling-bon d C(111) surface are very close in energy and domains of different rec onstructions can compete. These structures may explain recent scanning tunneling microscopy findings on films grown by chemical vapor deposi tion.