Actinium Hydrides AcH10, AcH12, and AcH16 as High-Temperature Conventional Superconductors

Stability of numerous unexpected actinium hydrides was predicted via evolutionary algorithm USPEX. Electron-phonon interaction was investigated for the hydrogen-richest and most symmetric phases: R$\overline{3}$m-$AcH_{10}$, I4/mmm-$AcH_{12}$ and P$\overline{6}$m2-$AcH_{16}$. Predicted structures of actinium hydrides are consistent with all previously studied Ac-H phases and demonstrate phonon-mediated high-temperature superconductivity with Tc in the range 204-251 K for R$\overline{3}$m-$AcH_{10}$ at 200 GPa and 199-241 K for P$\overline{6}$m2-$AcH_{16}$ at 150 GPa which was estimated by directly solving of Eliashberg equation. Actinium belongs to the series of d1-elements (Sc-Y-La-Ac) that form high-Tc superconducting (HTSC) hydrides. Combining this observation with p0-HTSC hydrides ($MgH_{6}$ and $CaH_{6}$), we propose that p0- and d1-atoms with low-lying empty orbitals tend to form phonon-mediated HTSC metal polyhydrides.