Quasi-chemical theory for anion hydration and specific ion effects: Cl-(aq) vs. F-(aq)

•In chloride-water clusters, H-bond between waters lead to anharmonicity.•Computations used here account for anharmonicity, agrees with gas-phase experiments.•Dynamics calculations reveal qualitative differences in hydrated halide clusters.•QCT partitioning of hydration free energy quantitatively captures those differences.