Possible lowest-energy geometry of silicon clusters Si21 and Si25.

Possible lowest-energy structures of Si21 and Si25 are found on the basis of the starting structures obtained via the global search for nearly identical low-energy Stillinger-Weber (SW) and modified-SW structures. The fact that the lowest-energy structures are spherical-like may suggest that the prolate-to-spherical-like structural transition for the silicon cluster Sin is likely to occur in the range of 21 < n < 25.