Regular Article

Micro hydration structure of aqueous Li⁺ by DFT and CPMD

¹ Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Qinghai 810008, P.R. China
² Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, Xining 810008, P.R. China
³ University of Chinese Academy of Sciences, Beijing 100049, P.R. China

^a e-mail: yongqzhou@163.com

Received: 14 May 2019
Received in final form: 29 October 2019
Published online: 9 January 2020

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 Å. Around 8.66 water with Li–O (I, W) distance of 4.10 Å from the second hydration shell. Both DFT and CPMD show Li⁺ possesses a second hydration shell which is dominantly surrounded by 8 water molecules.