Silicon oxide plays an important role in many technological areas. Extensive ab initio calculations for related systems are thus desired but are limited due to the requirement of a huge computation resource. We show here that an economic basis set can be used to determine reliable atomic and electronic structures of the silicon oxide system. Binding energies in a single-point energy calculation using a standard higher-level basis set on the geometric structures optimized with the economic basis set found reasonable agreement with reported ones of high-level calculations. The approach has enabled the computation of silicon oxide clusters as large as 16 atoms being performed with considerably high accuracy using a medium level of computation resources. (C) 2001 American Institute of Physics.