Ab initio molecular dynamics (AIMD) simulations. In totality, the present analysis of NMR data suggests that ion transport in lithium-ion conductors is affected by the isotopes. In particular, Li compounds have a higher activation barrier for ionic transport than the corresponding Li compounds. Irrespective of the different material compositions and crystal structures, this isotope effect persists. In order to further validate the experimental transport observations, as well as provide insights to the vibrational (phonon) dynamics of each compound, AIMD simulations were performed. Experimental crystal structures obtained from neutron diffraction measurements were used as a starting point to obtain the relaxed computational structures of both Li10SnP2S12 and Li6PS5Cl. The details of computation methods, including the evaluation of the diffusivity, can be found in the Supporting Information (Supplemental Note 3).