Complex dynamics of the Si(111)-7x7 surface: Total-energy calculations

We studied the dynamics of a semi-infinite Si(111)-7x7 system, using the force-constant matrix obtained from the total-energy calculation based on a nonorthogonal tight-binding Hamiltonian. We modeled the semi-infinite system by merging the optimized surface slab seamlessly onto the bulk to underscore the importance of the system size in obtaining all the relevant surface phonon modes of Si(111)-7x7. Our study has uncovered modes that have hitherto not been reported by ab initio molecular-dynamics studies and, also, provides detailed explanations of the nature of all important surface dynamical features (e.g., modes associated with dimers, adatoms, stacking faults, and rest atoms), using an analysis of the site density of states and pair density of states that identifies directly coupled vibrations.