Structural transition of Si clusters and their thermodynamics

The lowest energy structures of Si-n clusters up to 21 atoms are optimized with a genetic algorithm (GA) and density functional theory (DFT) with gene ralized gradient approximation (GGA). The structural transition from prolat e cage-based structures to near-spherical configurations is found at n = 17 . Remarkable different melting behaviors of silicon clusters are obtained b etween those in prolate structures and near-spherical geometries. The struc tural transformation of near-spherical clusters is observed in the melting process. Two possible melting processes are proposed: near-spherical --> pr olate --> subunits --> molten and near-spherical --> prolate --> molten obl ate. (C) 2001 Elsevier Science B.V. All rights reserved.