Theory of the “Honeycomb Chain-Channel” Reconstruction ofM/Si(111)-(3×1)

First-principles electronic-structure methods are used to study a structural model for $\mathrm{Ag}/\mathrm{Si}\left(111\right)$- $(3\times 1)$, recently proposed on the basis of transmission electron diffraction data. The fully relaxed geometry for this model is far more energetically favorable than any previously proposed, partly due to the unusual formation of a Si double bond in the surface layer. The calculated electronic properties of this model are in complete agreement with data from angle-resolved photoemission and scanning tunneling microscopy.