Li4PS 4I was recently discovered as a novel crystalline lithium ion conductor by applying a soft chemistry approach . It adopts a tetragonal structure type suggesting a three-dimensional migration pathway favorable for a high conductivity . Especially in view of the highly connected pathways for Li motion within a simple anion sublattice formed by P4(3-) and iodine anions, the conductivity measured from both impedance spectroscopy and NMR data appears to be rather small, and a negative influence of impurities and of grain boundaries effects was assumed.
Here we present ab initio calculations  on the structural and transport properties of this newly synthesized solid electrolyte. Using structural model that accounts for the partial occupancies determined by diffraction experiments, we calculate the diffusion coefficient and activation barrier for Li motion by analyzing molecular dynamics trajectories for both a crystalline and a glassy structure and also jump frequencies. We discuss the role of superbasins and correlation effects.
The analysis of crystalline and a glassy supercells implies that Li4PS4I is in fact a superionic conductor with a much higher conductivity than reported so far.
 S.J. Sedlmaier et al., Chem. Mater. 29 (2017) 1830
 S. Sicolo et al, Solid State Ionics, 319(2018) 83-91