Microsolvation of cationic alkali dimers in helium: quantum delocalization and solid-like/liquid-like behaviors of He shells

We performed path-integral molecular dynamics (PIMD) simulations in the NVT ensemble to investigate the quantum solvation of Li₂⁺ in He nanoclusters at a low temperature of 2 K. The interaction potentials were modeled using a sum-of-potentials approach, incorporating automated learning <i>ab initio</i>-based models up to three-body terms. Additionally, the semiclassical quadratic Feynman-Hibbs approach was applied to incorporate quantum effects into classical computations effectively, enabling the study of He_<i>N</i>Li₂⁺ complexes with up to 50 He atoms. The quantum simulations revealed strong evidence of local solid-like behavior in the He atoms within the first solvation shell surrounding the Li₂⁺ dimer cation. In contrast, the second and third solvation shells displayed delocalized He densities, allowing for the interchange of He atoms between these layers, indicative of a liquid-like structure. Our findings align with earlier studies of He-doped clusters, particularly in systems where the charged impurity interacts strongly with the solvent medium, significantly impacting the helium environment at the microscopic level.