How crucial are finite temperature and solvent effects on structure and absorption spectra of Si₁₀?

We have investigated finite temperature and solvent effects on the structure, and optical absorption properties of the Si₁₀ cluster, as a model for functionalized clusters used in biomedical applications. Among the many isomers possible for Si₁₀ clusters we have studied tetracapped trigonal prism (TCTP) with C_3v symmetry, which previously has been reported to be the global minimum structure, using the Car-Parrinello hybrid QM/MM technique. We observe that Si₁₀ remains to be in the TCTP structure in the gas phase, while in solvents we see dominant population of a distorted TCTP conformer which has a similar structure like TCTP except for one of the surface atoms changing its face center position to the edge. We find that there is frequent conformational transitions between these two structures. In the presence of solvents, the interatomic distances are lowered significantly compared to the case of gas phase. While solvent effects appear not to be very significant for the prediction of the excitation energy in the silicon cluster, we find that temperature effects have a substantial influence on its structure and optical properties.