Lithium ion-water clusters in strong electric fields: a quantum chemical study.

We use density functional theory to investigate the impact that strong electric fields have on the structure and energetics of small lithium ion-water clusters, Li(+)·nH2O, with n = 4 or 6. We find that electric field strengths of ∼0.5 V/Å are sufficient to break the symmetry of the n = 4 tetrahedral energy minimum structure, which undergoes a transformation to an asymmetric cluster consisting of three water molecules bound to lithium and one additional molecule in the second solvation shell. Interestingly, this cluster remains the global minimum configuration at field strengths ≳0.15 V/Å. The 6-coordinated cluster, Li(+)·6H2O, features a similar transition to 5- and 4-coordinated clusters at field strengths of ∼0.2 and ∼0.3 V/Å, respectively, with the tetra-coordinated structure being the global minimum even in the absence of the field. Our findings are relevant to understanding the behavior of the Li(+) ion in aqueous environments under strong electric fields and in interfacial regions where field gradients are significant.