Ab initiototal-energy calculations for extremely large systems: Application to the Takayanagi reconstruction of Si(111)

We have implemented a set of total-energy pseudopotential codes on a parallel computer which allows calculations to be performed for systems containing many hundreds of atoms in the unit cell. Using these codes, we have calculated the total energies and structures of the 33, 55, and 77 Takayanagi reconstructions of the (111) surface of silicon. We find that the 77 structure minimizes the surface energy and observe structural trends across the series which can be correlated with the degree of charge transfer between the dangling bonds on the adatoms and rest atoms.