First principles computer simulations of Li$_{10}$GeP$_2$S$_{12}$ and related lithium superionic conductors*

A recent paper by Kamaya {\em{et al.}}\footnote{ N. Kamaya {\em{et al.}}, {\em{Nature Materials}} {\bf{10}}, 682 (2011).} reported a new crystalline superionic conductor having a compact tetrahedral structure and a stoichiometry of Li$_{10}$GeP$_2$S$_{12}$. The room temperature conductivity was reported to be 0.01 S/cm, comparable to liquid electrolyte conductivies and five times higher the compositionally related thio-LISICON material Li$_{3.25}$Ge$_{0.25}$P$_{0.75}$S$_4$ developed earlier.\footnote{R. Kanno {\em{et al.}}, {\em{J. Electrochem. Soc.}} {\bf{148}}, A742 (2001).} This talk will present a progress report on our work to perform first principles computer simulations for these materials focussing on the structural, stability, and Li ion mobility properties of idealized crystalline models. From the perspective of our previous studies of Li ion conductivity in lithium thiophosphate electrolytes,\footnote{ N. A. W. Holzwarth {\em{et al.}}, {\em{J. Power Sources}} {\bf{196}}, 6870 (2011).} the effects of introducing Ge can be assessed.