An interatomic potential model for Si–Br systems has been developed for performing classical molecular dynamics (MD) simulations. This model enables us to simulate atomic-scale reaction dynamics during Si etching processes by Br+-containing plasmas such as HBr and Br2 plasmas, which are frequently utilized in state-of-the-art techniques for the fabrication of semiconductor devices. Our potential form is based on the well-known Stillinger–Weber potential function, and the model parameters were systematically determined from a database of potential energies obtained from ab initio quantum-chemical calculations using GAUSSIAN03. For parameter fitting, we propose an improved linear scheme that does not require any complicated nonlinear fitting as that in previous studies [H. Ohta and S. Hamaguchi, J. Chem. Phys. 115, 6679 (2001)]. In this paper, we present the potential derivation and simulation results of bombardment of a Si(100) surface using a monoenergetic Br+ beam.