Ab initio molecular orbital calculations were performed to simulate the elemental processes of the initial stage of the layer-controlled SiO2 growth on Si(001). The calculations produced good agreement with experimental results in terms of both adsorption and activation energy when no catalyst was present. On the other hand, when there was a catalyst, the calculations reproduced the general catalysis observed in the experiment, but the effects of the catalyst (i.e., the downward shift of the activation energy and the growth temperature compared to those of the noncatalyzed reaction) were somewhat underestimated in the calculations as compared with the experimental results.