  We recently proposed a new structural model for the Si(331)-(12x1) surface
reconstruction containing silicon pentamers as elementary structural building
blocks. Using first-principles density-functional theory we here investigate
the stability of a variety of adatom configurations and determine the lowest
energy configuration. We also present a detailed comparison of the energetics
between our model for Si(331)-(12x1) and the adatom-tetramer-interstitial model
for Si(110)-(16x2), which shares the same structural building blocks.
