Structures and relative stability of medium-sized silicon clusters.V.Low-lying endohedral fullerenelike clusters Si_(31)-Si_(40)and Si_(45)

摘要

We have performed unconstrained search for low-lying structures of medium-sized silicon clusters Si_(31)-Si_(40)and Si_(45),by means of the minimum-hopping global optimization method coupled with a density-functional based tight-binding model of silicon.Subsequent geometric optimization by using density-functional theory with the PBE,BLYP,and B3LYP functionals was carried out to determine the relative stability of various candidate low-lying silicon clusters obtained from the unconstrained search.The low-lying characteristics of these clusters can be affirmed by comparing the binding energies per atom of these clusters with previously determined lowest-energy clusters(Si_n)in the size range of 21 <=n<= 30.In view of the fact that there exist numerous low-lying"endohedral fullerenelike"isomers for each size in the range 30 <= n <= 40,we used the homologue carbon-fullerene cage to classify different families of isomers.This structural classification allows us to focus on generic features of various isomers and to group many apparently different isomers into a single family.In addition,we report a new family of low-lying clusters which have"Y-shaped three-arm"structures.Isomers in this"handmade"family can be energetically competitive as the endohedral fullerene isomers when the total energies are calculated with the BLYP or B3LYP functional.