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 ${\mathrm{Si}}_n$ ( $n=20,25\mathrm{}$) clusters. For $T=0\mathrm{}$ we solve the electronic structure by the density functional and the highly accurate quantum Monte Carlo approaches. Finite temperature and dynamical effects are investigated by the ab initio molecular dynamics method. This combination of methods enables us to find several new low-energy isomers and to explain the differences in properties, behavior, and stability of elongated versus compact types of structures and to elucidate the origin of the existing discrepancies between theory and experiments.