Prediction of quaternary hydrides based on densest ternary sphere packings

Abstract

We exhaustively search quaternary metal hydrides based on the (13-2-1) and (13-3-1) structures that are two of the putative densest ternary sphere packings in cubic systems [R. Koshoji et al., Phys. Rev. E 104, 024101 (2021)]. The 73 304 candidate hydrides are generated by substituting the small spheres with hydrogen atoms, and the medium, large, and fourth spheres with metallic atoms. Specifically, the substitution of the small spheres with hydrogen atoms gives the unconventional hydrogen sublattices. We screen unstable hydrides in the candidates through geometrical optimizations, constant pressure molecular dynamics simulations, and phonon calculations under hydrostatic pressure of 10 GPa, and identify 23 hydrides with static and dynamic stability, including ${\mathrm{H}}_{12}{\mathrm{ScY}}_{2}\mathrm{La}$ and ${\mathrm{H}}_{12}\mathrm{Ti}{\mathrm{Ni}}_{3}\mathrm{Ba}$. The superconducting transition temperatures ${T}_{c}$, calculated by density functional theory for superconductors, are found to be 5.7 and 6.7 K for the selected two hydrides ${\mathrm{H}}_{12}{\mathrm{ScY}}_{2}\mathrm{Ca}$ and ${\mathrm{H}}_{12}{\mathrm{ScY}}_{2}\mathrm{Sr}$, respectively. We expect that the 23 candidates of hydrides screened by the exhaustive search for 73 304 hydrides provide a guideline to narrow down the search space for trials in the experimental synthesis of quaternary metal hydrides.