Quasi-two-dimensional metallic hydrogen in diphosphide at a high pressure

The structural, electronic, phonon, and other characteristics of the normal phases of phosphorus hydrides with stoichiometry PH_k are analyzed. The properties of the initial substance, namely, diphosphine are calculated. In contrast to phosphorus hydrides with stoichiometry PH₃, a quasi-two-dimensional phosphorus-stabilized lattice of metallic hydrogen can be formed in this substance during hydrostatic compression at a high pressure. The formed structure with H–P–H elements is shown to be locally stable in phonon spectrum, i.e., to be metastable. The properties of diphosphine are compared with the properties of similar structures of sulfur hydrides.