Hydration of Kr(aq) in dilute and concentrated solutions

Molecular dynamics simulations of water with both multi-Kr and single Kr atomic solutes are carried out to implement quasi-chemical theory evaluation of the hydration free energy of Kr(aq). This approach obtains free energy differences reflecting Kr–Kr interactions at higher concentrations. Those differences are negative changes in hydration free energies with increasing concentrations at constant pressure. The changes are due to a slight reduction of packing contributions in the higher concentration case. The observed Kr–Kr distributions, analyzed with the extrapolation procedure of Krüger et al., yield a modestly attractive osmotic second virial coefficient, B2 ≈ -60 cm3/mol. Moreover, the thermodynamic analysis interconnecting these two approaches shows that they are closely consistent with each other, providing support for both approaches.