Nature of Alkali Ion-Water Interactions: Insights from Many-Body Representations and Density Functional Theory. II.

Interaction energies of alkali ion-water dimers, M(HO), and trimers, M(HO), with M = Li, Na, K, Rb, and Cs, are investigated using various many-body potential energy functions and exchange-correlation functionals selected across the hierarchy of density functional theory approximations. Analysis of interaction energy decompositions indicates that close-range interactions such as Pauli repulsion, charge transfer, and charge penetration must be captured in order to reproduce accurate interaction energies. In particular, it is found that simple classical polarizable models must be supplemented with dedicated terms which account for these close-range interactions in order to achieve chemical accuracy.

Nature of Halide-Water Interactions: Insights from Many-Body Representations and Density Functional Theory.

Interaction energies of halide-water dimers, X(HO), and trimers, X(HO), with X = F, Cl, Br, and I, are investigated using various many-body models and exchange correlation functionals selected across the hierarchy of density functional theory (DFT) approximations. Analysis of the results obtained with the many-body models demonstrates the need to capture important close-range interactions in the regime of large intermolecular orbital overlap, such as charge transfer and charge penetration. Failure to reproduce these effects can lead to large deviations relative to reference data calculated at the coupled cluster level of theory.