The initial adsorption mechanism of TiCl4 on H/Si(100)-2 x 1 surface was theoretically studied. The direct chlorination channel turned out to be kinetically the most favorable on H/Si(100)-2 x 1 surface, contrasting to the corresponding reactions on OH/Si(100)-2 x 1. Consequently, it would increase the surface Cl/Ti ratio. (C) 2008 Elsevier B.V. All rights reserved.