Silicon clusters of intermediate size: Energetics, dynamics, and thermal effects

A combination of the best available theoretical techniques for energetics, dynamics, and thermodynamics is employed in an extensive study of Si-n (n = 20, 25) clusters. For T = 0 we solve the electronic structure by the densi ty functional and the highly accurate quantum Monte Carlo approaches. Finit e temperature and dynamical effects are investigated by the ab initio molec ular dynamics method. This combination of methods enables us to find severa l new low-energy isomers and to explain the differences in properties, beha vior, and stability of elongated versus compact types of structures and to elucidate the origin of the existing discrepancies between theory and exper iments.