Proton-Induced Plasticity in Hydrogen Clusters

The effect of protonation of pure hydrogen clusters is investigated at low temperature using a combination of path-integral simulations and first-principles electronic structure calculations. The added proton gets trapped as a very localized ${\mathrm{H}}_3^{+}$ impurity in the cluster core, and is surrounded by stable shells of solvating ${\mathrm{H}}_2$ molecules. These clusters are frozen with respect to the translational degrees of freedom, while the ${\mathrm{H}}_2$ ligands undergo large-amplitude rotations. The classical approximation for the nuclei fails to account for this effect which is akin to plastic behavior in crystals.