Nanosecond quantum molecular dynamics simulations of the lithium superionic conductorLi4−xGe1−xPxS4

Abstract

The microscopic origin of high conductivity at room temperatures in lithium superionic conductors has remained a fundamental unsolved problem, although the recent discovery of ${\mathrm{Li}}_{10}$${\mathrm{GeP}}_{2}$${\mathrm{S}}_{12}$ was a great step toward the application of solid electrolytes. We achieve long-time (2-ns) tight-binding molecular dynamics simulations of ${\mathrm{Li}}_{4\ensuremath{-}x}$${\mathrm{Ge}}_{1\ensuremath{-}x}$${\mathrm{P}}_{x}$${\mathrm{S}}_{4}$ and observe the diffusion process where lithium atoms collectively hop into neighboring lithium sites by kicking the lithium atoms occupying these sites out. Furthermore, it is found that excess lithium atoms or doped lithium vacancies trigger a new diffusion process and drastically reduce the activation energy. We discuss the dynamic properties of lithium atoms in these materials, such as the diffusion constant, the activation energy, and the diffusion path.