Designing Quaternary Hydrides with Potential High T_c Superconductivity

We propose three parent structures for designing quaternary hydrides of increasing complexity to optimize parameters correlated with high T_c superconductivity. The first is a simple Pm3m cell inspired by the FCC RH_3 structures (R = trivalent rare earths), which we show has moderately promising potential for high T_c compounds. The second is an Fm3m heterostructure inspired by our work on Lu_8H_23N that consistently produces metallic hydrogen sublattices, whose quantum interference with Lewis bases is designed to high DOS_H(E_F). Several examples are put forward that first-principles calculations confirm have hydrogen-dominant metal character, as well as strong network connectivity as measured with the Electron Localization Function (ELF). The third quaternary model structure allows for a more precise description of doping as well as symmetry breaking of octahedral hydrogen which improves the hydrogen network connectivity. These model structures/formulae predict compounds with high predicted T_c and have enough flexibility to optimize for both T_c and stability at low pressures.