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 calculations for the extended Pandey model and the Seiwatz model. Even though the extended Pandey model is favored on the basis of scanning tunneling microscopy and total-energy considerations, the calculated surface states are inconsistent with experiment. The calculated states for the Seiwatz model are consistent with the experimental dispersion along the main symmetry direction (<(Gamma)over bar> (A) over bar) but serious discrepancies exist in other parts of the Brillouin zone. The disparity between the density-functional-theory calculations and experiment indicate that exchange and correlation in pi-bonded Si chains may need to be analyzed beyond the mean-field band-structure approach.