Affiliations: Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085, India | [x] Department of Chemistry, University of Patras, Greece | [y] Department of Physics, University of Patras, Greece
Abstract: The geometric and electronic structures of Sin, Sin+, Sin−, AlSin−1 and PSin−1 clusters (2⩽n⩽13) has been investigated using the ab initio molecular orbital theory under the density functional theory formalism. Relative stabilities of these clusters have been analyzed based on their binding energies, second difference in energy (Δ2E) and fragmentation behavior. The equilibrium geometry of the neutral and charged Sin clusters shows similar structural growth. The geometries of the Sin+ and AlSin−1 are similar to those of the Sin, but with small distortions. The ground state geometries of the AlSin−1 clusters shows that the impurity Al atom prefers to substitute for the Si atom, that has the highest coordination number in the host Sin cluster. However for Sin−, n=6, 8, 11, and 13, significant changes have been observed in the ground state geometries of the negatively charged clusters as compared to their neutral counterparts. In general the geometries of the P substituted silicon clusters remain similar to that of negatively charged Sin clusters with small local distortions. In general, the average binding energy of charged clusters is found to be higher than that of neutral Sin clusters. However, significant differences have been observed in the electronic structure of neutral and charge cluster leading to their different stability pattern. While for neutral clusters, the Si10 is magic, the extra stability of the Si11+ cluster over the Si10+ and Si12+bears evidence for the magic behavior of the Si11+ cluster, which is in excellent agreement with the recent experimental observations (ref. [29]). Similarly for AlSin−1 clusters, which is iso-electronic with Sin+ clusters show extra stability of the AlSi10 cluster suggesting the influence of the electronic structures for different stabilities between neutral and charged clusters. For iso-electronic PSin−1 clusters, it is found that although for small clusters (n<4) substitution of P atom improves the binding energy of Sin clusters but for larger clusters (n>4), the effect is opposite. The fragmentation behavior of all these clusters shows that while small clusters prefers to evaporate monomer, the larger ones dissociates into two stable clusters of smaller size. Finally, a good agreement between experimental and our theoretical results suggests good prediction of the lowest energy isomeric structures for all clusters calculated in the present study.
