Equilibrium Structures and Absorption Spectra for SixOy-nH2O Molecular Clusters using Density Functional Theory

Calculations are presented of vibrational and electronic excited-state absorption spectra for equilibrium structures of SixOy-nH2O molecular clusters using density function theory DFT and time-dependent density functional theory TD-DFT. The size of the clusters considered is relatively large compared to those considered in previous studies. DFT and TD-DFT can provide interpretation of absorption spectra with respect to molecular structure for excitation by electromagnetic waves at frequencies within the IR and UV-visible ranges. The absorption spectrum corresponding to excitation states of SixOy-nH2O molecular clusters consisting of relatively small numbers of atoms should be associated with response features that are intermediate between that of isolated molecules and that of a bulk system. DFT and TD-DFT calculated absorption spectra represent quantitative estimates that can be correlated with additional information obtained from laboratory measurements. The DFT software GAUSSIAN was used for the calculations of excitation states presented here.