Solvation of Potassium Cation in Helium Clusters: Density Functional Theory versus Pairwise Method

Abstract Microsolvation of a cation in helium quantum solvent is an attractive phenomenon leading generally to the formation of a strongly packed structure known as 'Snowball' feature. Here, the lowest energy structures and the relative stability of the solvated potassium cation K+ in helium clusters K+Hen up to the size n = 20 are investigated employing Density Functional Theory (DFT) and pairwise methods. The DFT calculations showed that M05-2X/6-311++G(3df,2p) level of theory can reproduce properly the experimental data of K+He diatomic potential, whereas, in the pairwise method, the Basin-Hopping Monte Carlo (BHMC) algorithm was applied for the global optimization. The remarkable differences in the lowest energy structures computed in the frame of both methods are shown for K+He11 and K+He12 clusters. The BHMC optimization converged to an icosahedral geometry for n=12, corresponding to the highest value of the binding energy per atom. For both methods, we have concluded that the first solvation shell is completed at the size n = 15, despite the maximum packing structure obtained at n = 17. Finally, the stability of the potassium doped helium cluster is discussed based on the Density Of States (DOS) curves.