Prediction of a stable helium-hydrogen compound: First-principles simulations

Abstract

Despite extensive experimental and theoretical work, consensus on the crystal structure and stability of the helium-hydrogen system is lacking. In this study, we investigate the possibility of helium forming a stable compound with hydrogen by using a first-principles structure search method. As a result of first-principles simulations, we predict a helium-hydrogen compound that is mechanically stable below 8 GPa with a $\mathrm{He}{({\mathrm{H}}_{2})}_{3}$ stoichiometry. Topological analysis of electron density at the bond critical points shows that there exists a quantifiable level of van der Waals interaction between helium and hydrogen in this $\mathrm{He}{({\mathrm{H}}_{2})}_{3}$ crystal. Our current results provide a case of weak interaction in a mixed hydrogen-helium system, offering insights for the evolution of interiors of giant planets such as Jupiter and Saturn.