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 H-3(+) impurity in the cluster core, and is surrounded by stable shells of solvating H-2 molecules. These clusters are frozen with respect to the translational degrees of freedom, while the 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.