THEORY OF THE HONEYCOMB CHAIN-CHANNEL RECONSTRUCTION OF M SI(111)-(3X1)/

First-principles electronic-structure methods are used to study a stru ctural model for Ag/Si(111)-(3 x 1), recently proposed on the basis of transmission electron diffraction data. The fully relaxed geometry fo r this model is far more energetically favorable than any previously p roposed, partly due to the unusual formation of a Si double bond in th e surface layer. The calculated electronic properties of this model ar e in complete agreement with data from angle-resolved photoemission an d scanning tunneling microscopy.