Using the density-functional theory, combined with the nudged elastic band method, migration pathways were calculated and the activation energy barriers for the diffusion of Ag ions in low-temperature Ag2S were estimated. The activation energy barriers for 4 essential migrations of an Ag ion: from a tetrahedral (T) site to an adjacent T vacancy (VT), from an octahedral (O) site to an adjacent O vacancy (VO), from T to VO, and from O to VT, were estimated to be: 0.461, 0.668, 0.212 and 0.318eV, respectively. These were comparable with experimental values. This implied that the diffusion of Ag ions between non-equivalent sites was preferred to that between equivalent sites, and that direct T-VT and O-VO diffusion was less likely to occur than was indirect T-VO-T and O-VT-O diffusion. These diffusion paths between non-equivalent sites were also supported by ab initio molecular dynamics simulations, in which the diffusion pathways were directly observed. Migration of Ag in Low-Temperature Ag2S from First Principles. Z.Wang, T.Gu, T.Kadohira, T.Tada, S.Watanabe: Journal of Chemical Physics, 2008, 1281[1], 014704