title: Ab Initio Study of Ionized Water Radical Cation (H2O)8+in Combination with the Particle Swarm Optimization Method.
abstract: The structures of cationic water clusters (H2O)8+have been globally explored by the particle swarm optimization method in combination with quantum chemical calculations. Geometry optimization and vibrational analysis for the 15 most interesting clusters were computed at the MP2/aug-cc-pVDZ level and infrared spectrum calculation at MPW1K/6-311++G** level. Special attention was paid to the relationships between their configurations and energies. Both MP2 and B3LYP-D3 calculations revealed that the cage-like structure is the most stable, which is different from a five-membered ring lowest energy structure but agrees well with a cage-like structure in the literature. Furthermore, our obtained cage-like structure is more stable by 0.87 and 1.23 kcal/mol than the previously reported structures at MP2 and B3LYP-D3 levels, respectively. Interestingly, on the basis of their relative Gibbs free energies and the temperature dependence of populations, the cage-like structure predominates only at very low temperatures, and the most dominating species transforms into a newfound four-membered ring structure from 100 to 400 K, which can contribute greatly to the experimental infrared spectrum. By topological analysis and reduced density gradient analysis, we also investigated the structural characteristics and bonding strengths of these water cluster radical cations.
authors.affiliation: Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu 610065, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Tang
authors.affiliation: College of Physics and Electronic Engineering, Chongqing Normal University , Chongqing 400047, China.
authors.forename: Cui-E
authors.initials: CE
authors.lastname: Hu
authors.affiliation: Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu 610065, China.
authors.forename: Zhen-Long
authors.initials: ZL
authors.lastname: Lv
authors.affiliation: Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu 610065, China.
authors.forename: Xiang-Rong
authors.initials: XR
authors.lastname: Chen
authors.affiliation: National Key Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics , Mianyang 621900, China.
authors.forename: Ling-Cang
authors.initials: LC
authors.lastname: Cai