Ab initiotheory of the Si(111)-(7×7) surface reconstruction: A challenge for massively parallel computation

An ab initio investigation of the Si (111) - (77) surface reconstruction is undertaken using the state of the art in massively parallel computation. Calculations of the total energy of an 700 effective-atom supercell are performed to determine (1) the fully relaxed atomic geometry, (2) the scanning-tunneling-microscope images as a function of bias voltage, and (3) the energy difference between the (77) and the (21) reconstructions. The (77) reconstruction is found to be energetically favorable to the (21) surface by 60 meV per (11) unit cell.