Li+？Li+ and Na+？Li+ ion pairs in aqueous solution

Abstract

Like ion pair Li+-Li+ and mix ion pair Na+-Li+ in aqueous solution were investigated by high level ab initio calculation and quantum mechanical effective fragment potential molecular dynamics (QM/EFP MD). Our QM/ EFP-MD predicts that like ion pair Li+-Li+ are more likely to be observed than mix ion pair Na+-Li+ in the solution. In a particular, the formation of Li+-Li+ is less than that of Na+-Na+, and the formation of Na+-Li+ is even worse. The local structural analysis indicates that three-water bridging structure is dominating in Li+-Li+ion pair in the solution whereas the Na+-Li+ ion pair mostly bound to one water molecule. Both the MD and QM study suggests that one water bridging structure is very unstable.