The Physicochemical Characteristics of Silicon-Germanium Nanoclusters

Abstract

A systematic investigation with density functional theory (DFT) was carried out in order to explore the structural, energetic and electronic properties of silicon-doped germanium (SiGen, n  1-20) clusters using SIESTA package. In this regard, isomers of SiGen clusters with the lowest-energy were determined and discussed. We found that the doping of Gen + 1 clusters with one Si atom enhances the stability of these clusters. The relative stability has been studied relative to cluster size in terms of binding energies, fragmentation energies and second-order difference of energies for all SiGen structures. Likewise, electronic properties such as HOMO-LUMO gaps, vertical electron affinity (VEA) and vertical ionization potential (VIP) were identified and analyzed as well. Maximum peaks of the fragmentation energy were observed at sizes n  3, 5, 8-11, 13, 15, and 17 for Gen + 1 and SiGen clusters, respectively, which indicates that these clusters have higher relative stability than their neighbors. Besides, the second energy difference analysis shows that Gen + 1 and SiGen clusters at n  2-8, 10-15, 19, 20 are more stable. The values of HOMO-LUMO gaps take a decreasing trend with the increasing number of Si atoms in the cluster, which suggest an increase in chemical activity. Also, through our discussion of parameters VEA and VIP we found that SiGe4 cluster has high metallic property. The obtained results revealed that the SiGe15 cluster with C2 symmetry is more stable than the other clusters.