Structural, electronic, and vibrational properties of Si(111)-2×1 from ab initio molecular 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 (2×1) 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.