Search for high-Tc conventional superconductivity at megabar pressures   in the lithium-sulfur system
  Motivated by the recent report of superconductivity above 200 K in ultra-dense hydrogen sulfide, we search for high-\tc\ conventional superconductivity in the phase diagram of the binary Li-S system, using {\em ab-initio} methods for crystal structure prediction and linear response calculations for the electron-phonon coupling. We find that at pressures higher than 20 GPa, several new compositions, besides the known Li$_2$S, are stabilized; many exhibit electride-like {\em interstitial} charge localization observed in other alkali metal compounds. Of all predicted phases, only Li$_3$S at P > 640 GPa displays a sizable \tc, in contrast to what is observed in sulfur and phosphorus hydrides, where several stoichiometries lead to high \tc. We attribute this difference to 2$s$-2$p$ hybridization and avoided core overlap, and predict similar behavior for other alkali metal compounds. 
Christian Kokail (1), Christoph Heil (2) and Lilia Boeri (1) ((1)   Institute of Theoretical and Computational Physics, Graz...
cond-mat.supr-con cond-mat.mtrl-sci