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<p>A systematic analysis of the hydration structure of Cs+ ions in solution is derived from
simulations carried out using a series of molecular models built upon a hierarchy of
approximate representations of many-body effects in ion-water interactions. It is found
that a pairwise-additive model, commonly used in biomolecular simulations, provides
poor agreement with experimental X-ray spectra, indicating an incorrect description of
the underlying hydration structure. Although the agreement with experiment improves
in simulations with a polarizable model, the predicted hydration structure is found
to lack the correct sequence of water shells. Progressive inclusion of explicit many-
body effects in the representation of Cs<sup>+</sup>-water interactions as well as account for
nuclear quantum effects is shown to be necessary for quantitatively reproducing the
experimental spectra. Besides emphasizing the importance of many-body effects, these
results suggests that molecular models rigorously derived from many-body expansions
hold promise for realistic simulations of aqueous solutions.
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Many-body effects in models with superexponential interactions
