Structural, electronic, and vibrational properties of Si(111)-2×1 fromab initiomolecular dynamics

We present the results of an ab initio molecular-dynamics study of the Si (111) surface at low temperatures. Our findings for the equilibrium structure confirm the Pandey (21) chain model and are in very good agreement with both low-energy electron diffraction and medium-energy ion-scattering data, showing in particular a large buckling of the surface chains. We describe the dynamical path followed during the reconstruction from the ideal bulk-terminated surface, which is found to be unstable. The phonon spectrum, which is calculated ab initio for the first time, shows well-defined surface modes at frequencies close to the measured values.