Quantum-Chemical Study of Phosphorus Effect on Properties of Small Silicon Clusters

This study has investigated phosphorus effect on the properties of small silicon clusters through the determination of optimized molecular structures, fragmentation energies, dissociation energies, energy gaps between the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, and formation energies of the pure clusters SiN and doped clusters with a single phosphorus atom SiN-1P (N ≤ 13) by means of hybrid density functional theory (DFT=B3LYP) method. The basis sets used in this work split-valence with double-(xi) plus polarization quality with additional diffuse functions, denoted [ 6-31++G(3d)]. Especially stable structures for Si6 and Si10 coincide with observed abundances in the experimental mass spectra and this result is similar to the corresponding result of other quantum-chemical studies. It is also found that the doping with phosphorus lead to a considerable decrease in the energy gap between the highest occupied molecular orbital (HOMO) level and lowest unoccupied molecular orbital (LUMO) level and to a strongly changes in the optical properties. These results are also in agreement with the results of PL measurements.