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The hydrochlorination process is a necessary technological step for the production of polycrystalline silicon using the Siemens method. In this work, the adsorption behaviors of silicon tetrachloride (SiCl 4 ), silicon dichloride (SiCl 2 ), dichlorosilane (SiH 2 Cl 2 ), trichlorosilane (SiHCl 3 ), HCl, and H 2 on the Si(100) surface were investigated by first-principles calculations. The different adsorption sites and adsorption orientations were taken into account. The adsorption energy, charge transfer, and electronic properties of different adsorption systems were systematically analyzed. The results show that all of the molecules undergo dissociative chemisorption at appropriate adsorption sites, and SiHCl 3 has the largest adsorption strength. The analysis of charge transfer indicates that all of the adsorbed molecules behave as electron acceptors. Furthermore, strong interactions can be found between gas molecules and the Si(100) surface as proved by the analysis of electronic properties. In addition, SiCl 2 can be formed by the dissociation of SiCl 4 , SiH 2 Cl 2 , and SiHCl 3 . The transformation process from SiCl 4 to SiCl 2 is exothermic without any energy barrier. While SiH 2 Cl 2 and SiHCl 3 can be spontaneously dissociated into SiHCl 2 , SiHCl 2 should overcome about 110 kJ/mol energy barrier to form SiCl 2 . Our works can provide theoretical guidance for hydrochlorination of SiCl 4 in the experimental method., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)