Depressurization of Si from its metallic beta-Sn modification results
in a dense metastable form (Si-III), which is semimetallic and persist
s indefinitely at ambient pressure. We have investigated possible reco
nstructions of the Si-III (001) surface using ab initio pseudopotentia
l calculations and find that a configuration comprised of adatoms and
symmetric dimers has, to the best of our knowledge, a lower surface en
ergy than any other previously reported surface of silicon.