On the basis of ZINDO methods, according to the sum-over-states (SOS) expression, we divise the program for the calculation of nonlinear second-order optical susceptibilities βijk and study how the different substituents on the phenyl ring attached to the atom silicon influence on the nonlinear second-order optical properties for substituted silanes series molecules. The property of (CH3)3Si is studied particularly. The effect of length of silica chains on the calculated β values is studied too. The regularity summarized from calculated results has been explained micromechanically.

Key words: OPTICAL PROPERTIES, SILANE P, NON LINEAR OPTICS