BAND DISPERSIONS OF THE PI-BONDED-CHAIN RECONSTRUCTION OF SI(111)3X1-LI - A CRITICAL-EVALUATION OF THEORY AND EXPERIMENT

The surface-state band-structure of the three-domain Si(111) 3 x 1-Li reconstruction has been determined using angle-resolved photoemission. Experimental band dispersions are compared to theoretical calculation s for the extended Pandey model and the Seiwatz model. Even though the extended Pandey model is favored on the basis of scanning tunneling m icroscopy and total-energy considerations, the calculated surface stat es are inconsistent with experiment. The calculated states for the Sei watz model are consistent with the experimental dispersion along the m ain symmetry direction (<(Gamma)over bar> (A) over bar) but serious di screpancies exist in other parts of the Brillouin zone. The disparity between the density-functional-theory calculations and experiment indi cate that exchange and correlation in pi-bonded Si chains may need to be analyzed beyond the mean-field band-structure approach.