Si(111): (2 × 1) reconstruction and surface phonons fromab-initiomolecular dynamics

We present results of ab-initio Molecular Dynamics simulations of the Si(III) surface. Pandey's 2 x 1 chain-geometry is obtained by simulated annealing, starting directly from the ideal bulk-terminated surface. The dynamical path followed during the reconstruction is described. The resulting 2 x 1 structure agrees well with Low Energy Electron Diffraction and Medium Energy Ion Scattering results. The phonon spectrum which is calculated ab-initio for the first time shows well defined surface modes at frequencies close to the measured values. The atomic motions and the dynamic effective charges of these modes are also analyzed.