Global geometry optimization of silicon clusters described by three empirical potentials

The basic-hopping global optimization technique developed by Wales and Doye is employed to study the global minima of silicon clusters Si-n(3less than or equal tonless than or equal to30) with three empirical potentials: the Stillinger-Weber (SW), the modified Stillinger-Weber (MSW), and the Gong potentials. For the small-sized SW and Gong clusters (3less than or equal tonless than or equal to15), it is found that the global minima obtained based on the basin-hopping method are identical to those reported by using the genetic algorithm [Iwamatsu, J. Chem. Phys. 112, 10976 (2000)], as well as with those by using molecular dynamics and the steepest-descent quench (SDQ) method [Feuston, Kalia, and Vashishta, Phys. Rev. B 37, 6297 (1988)]. However, for the mid-sized SW clusters (16less than or equal tonless than or equal to20), the global minima obtained differ from those based on the SDQ method, e.g., the appearance of the endohedral atom with fivefold coordination starting at n=17, as opposed to n=19. For larger SW clusters (20less than or equal tonless than or equal to30), it is found that the bulklike endohedral atom with tetrahedral coordination starts at n=20. In particular, the overall structural features of SW Si-21, Si-23, Si-25, and Si-28 are nearly identical to the MSW counterparts. With the SW Si-21 as the starting structure, a geometric optimization at the B3LYP/6-31G(d) level of density-functional theory yields an isomer similar to the ground-state- isomer of Si-21 reported by Pederson [Phys. Rev. B 54, 2863 (1996)]. (C) 2003 American Institute of Physics.