Pressure-induced superconductivity in H(2)-containing hydride PbH(4)(H(2))(2)

High pressure structure, stability, metallization, and superconductivity of PbH(4)(H(2))(2), a H(2)-containing compound combining one of the heaviest elements with the lightest element, are investigated by the first-principles calculations. The metallic character is found over the whole studied pressure range, although PbH(4)(H(2))(2) is metastable and easily decompose at low pressure. The decomposition pressure point of 133 GPa is predicted above which PbH(4)(H(2))(2) is stable both thermodynamically and dynamically with the C2/m symmetry. Interestedly, all hydrogen atoms pairwise couple into H(2) quasi-molecules and remain this style up to 400 GPa in the C2/m structure. At high-pressure, PbH(4)(H(2))(2) tends to form the Pb-H(2) alloy. The superconductivity of T(c) firstly rising and then falling is observed in the C2/m PbH(4)(H(2))(2). The maximum of T(c) is about 107 K at 230 GPa. The softening of intermediate-frequency phonon induced by more inserted H(2) molecules is the main origin of the high T(c). The results obtained represent a significant step toward the understanding of the high pressure behavior of metallic hydrogen and hydrogen-rich materials, which is helpful for obtaining the higher T(c).