Theoretical studies on the structures and properties of As-doped Sin (n = 1–8) clusters

The As-doped small silicon clusters AsSi_n/${\text{AsSi}}_n^{+}/{\text{AsSi}}_n^{-}$ (n = 1–8) have been systematically investigated at the B3LYP/6–311+G^* level of theory. The most stable isomer of the neutral AsSi₂ cluster has an isosceles triangle structure (2n − 1). Edge-capping with a silicon atom to 2n − 1, yields the lowest energy structure of the neutral AsSi₃ cluster, a deformed planar rhombus structure (3n − 1). The ground state structure of the neutral AsSi₄ cluster is predicted to have a trigonal bipyramid form (4n − 1). Adding one, two, or three Si atoms to different positions in this 4n − 1 structure gives the lowest energy structures of the neutral AsSi₅, AsSi₆, and AsSi₇ clusters (5n − 1, 6n − 1, and 7n − 1), respectively. The global minimum of neutral AsSi₈ (8n − 1) can be gained by capping the most stable AsSi₇ structure with a silicon atom. The ground states of the neutral AsSi_n clusters are all doublet. The three low-energy states of ionic ${\text{AsSi}}_n^{+}/{\text{AsSi}}_n^{-}$ have very similar structures to those of their neutral AsSi_n counterparts, but their orders of stability are somewhat changed. Except for the smaller AsSi⁺, the most stable ${\text{AsSi}}_n^{+}/{\text{AsSi}}_n^{-}$ isomers all have singlet electronic states. Based on the optimized geometries, various energetic properties, including the incremental binding energies, the gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital, the adiabatic ionization potentials, and electron affinities, are calculated for the most stable isomers of AsSi_n/${\text{AsSi}}_n^{+}/{\text{AsSi}}_n^{-}$. All the results indicate that ${\text{AsSi}}_4^{-}$ and ${\text{AsSi}}_7^{-}$ have the highest stability of the investigated clusters. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds should be responsible for stabilizing the low-energy AsSi_n/${\text{AsSi}}_n^{+}/{\text{AsSi}}_n^{-}$ structures.