Ground-state path integral Monte Carlo simulations of positive ions in ${}^4$He clusters: bubbles or snowballs?

Abstract

The local order around alkali (Li${}^{+}$ and Na${}^{+}$) and alkaline-eath (Be${}^{+}$, Mg${}^{+}$ and Ca${}^{+}$) ions in ${}^4$He clusters has been studied using ground-state path integral Monte Carlo calculations. We apply a criterion based on multipole dynamical correlations to discriminate between solid-like versus liquid-like behavior of the ${}^4$He shells coating the ions. As it was earlier suggested by experimental measurements in bulk ${}^4$He, our findings indicate that Be${}^{+}$ produces a solid-like ("snowball") structure, similarly to alkali ions and in contrast to the more liquid-like ${}^4$He structure embedding heavier alkaline-earth ions.

9 pages, 12 figures