Calculations of linear and nonlinear optical properties of H-silsesquioxanes

We report the frequency dependence of linear and nonlinear optical suscepti bilities of H-silsesquioxanes of various cage sizes and conformations using the INDO/CI method coupled with the SOS method. The average dynamic refrac tive index of silsesquioxanes is found to decrease as the cage size increas es, and its variation is very small for the different conformations of the same cage size at the same incident wavelength. The calculated second-order susceptibilities show that small cages have a larger magnitude which is co mparable to that of crystalline alpha-quartz. It is suggested here that H-s ilsesquioxanes of a smaller cage size can be a good candidate materials for nonlinear optical applications having low absorption, wide transparency an d adequate susceptibility in ultraviolet or vacuum ultraviolet region of th e spectrum.