Computational molecular dynamics simulations of cationic alkali dimers solvated in He clusters: the Li₂⁺ case

The structures and energetics of Li-2(+) -doped He clusters have been determined by means of evolutionary programming optimizations and classical molecular dynamics simulations. The underlying interactions in the HeNLi+ 2 complexes are described by sum-of-potentials ab initio-based models. The classical picture of the He atoms surrounding the cationic dimer shows a selective growth of the clusters. By analyzing spatial distribution probabilities, and single-atom evaporative energies from molecular dynamics calculations, we found pronounced drops in the computed energy for N = 2, 4 and 6, and smaller ones for N = 10, 13, 15, 18, 20, 22, 24, 27 and 29. The most energetic favored structure (compared to its neighbors) is found when six He atoms are attached in the Li+ (2) -cation, forming He3-motifs at each side and leading to the formation of the first solvation shell. In turn, as extra He atoms are added, a new shell is started to form at N = 10, with the He3 triangles being the building blocks in all classical solid-like structural arrangements in HeNLi+ (2) clusters. By combining the outcome of our work on the existence of such local solvation microstructures in Li+ (2) -doped He clusters together with those from previous studies on alkali ions, we may speculate that such microsolvation effects could influence the short-time solute-solvent dynamics and thus contribute to the observed slow ions' mobility in He droplets.