Micro hydration structure of aqueous Li+ by DFT and CPMD

Abstract

Systematic study on microscopic hydration structure of lithium ion hydrated clusters, [Li(H2O)n]+ (n = 1–20), was carried out by density functional theory (DFT) calculations at ωB97XD/6-311++G(d,p) basis l evel and Car-Parrinello molecular dynamics. The DFT calculation results reveal that the four-coordinated structure is the favorable first hydration sphere for [Li(H2O)n]+ (n = 1–20) clusters in the aqueous phase. The second hydration layer of Li+ is 8 water molecules when n ≥ 12. The energy parameters calculation shows that the structures of the first and second hydration shells are relatively steady. For n > 9, the competitive effects of the second and third hydration layers on water molecules arise and the solvent-solvent interactions for outer hydration shell are strengthened. The results of bond parameters declare that the structure of inner hydration shell has little influence on the H2O molecules of outer hydration layer when the first and second hydration spheres of Li+ are saturated. MD simulation results prove Li+ has a strong first hydration shell with Li–O (I, W) distance of 1.970 A. Around 8.66 water with Li–O (I, W) distance of 4.10 A from the second hydration shell. Both DFT and CPMD show Li+ possesses a second hydration shell which is dominantly surrounded by 8 water molecules.