Unexpected Ag-H bond in the predictive silver hydride phase under high pressure

Abstract

Silver, typically acknowledged for its inertness toward hydrogen under standard conditions, exhibits a noteworthy shift in reactivity under elevated pressures. Employing first-principles variable-composition evolutionary search calculations, our investigation unveils the presence of thermodynamically stable Ag-H compounds. A novel stoichiometry, Ag2H, characterized by P3¯m1 symmetry, emerges as the thermodynamically stable phase at 100 GPa. Notably, the trigonal-Ag2H phase at 100 GPa demonstrates both mechanical and dynamic stability, as ascertained through the computation of elastic constants and phonon dispersions, respectively. Examination of the electronic band structure and density of states manifests the metallic nature of the resulting Ag2H compound. A comprehensive analysis involving crystal orbital bond index, Bader charge, and charge density plots substantiates the ionic character of Ag2H, attributable to effective charge transfer from silver atoms to hydrogen. Furthermore, application of the Allen-Dynes modified McMillan equation indicates the absence of superconducting behavior in Ag-H systems at the elevated pressure of 100 GPa.