Comparison of the Growth Patterns of Sinand GenClusters (n= 25−33).

We performed an unbiased search for low-energy structures of medium-sized neutral Si nand Ge nclusters ( n= 25−33) using a genetic algorithm (GA) coupled with tight-binding interatomic potentials. Structural candidates obtained from our GA search were further optimized by first-principles calculations using density functional theory (DFT). Our approach reproduces well the lowest-energy structures of Si nand Ge nclusters of n= 25−29 compared to previous studies, showing the accuracy and reliability of our approach. In the present study, we pay more attention to determine low-lying isomers of Si nand Ge n( n= 29−33) and study the growth patterns of these clusters. The B3LYP calculations suggest that the growth pattern of Si n( n= 25−33) clusters undergoes a transition from prolate to cage at n= 31, while this transition appears at n= 26 from the PBE-calculated results. In the size range of 25−33, the corresponding Ge nclusters hold the prolate growth pattern. The relative stabilities and different structural motifs of Si nand Ge n( n= 25−33) clusters were studied, and the changes of small cluster structures, when acting as building blocks of large clusters, were also discussed. [ABSTRACT FROM AUTHOR]