An understanding of density fluctuations in bulk water has made significantcontributions to our understanding of the hydration and interactions ofidealized, purely repulsive hydrophobic solutes. To similarly inform thehydration of realistic hydrophobic solutes that have dispersive interactionswith water, here we characterize water density fluctuations in the presence ofattractive fields that correspond to solute-water attractions. We find thatwhen the attractive field acts only in the solute hydration shell, but not inthe solute core, it does not significantly alter water density fluctuations inthe solute core region. We further find that for a wide range of solute sizesand attraction strengths, the free energetics of turning on the attractivefields in bulk water are accurately captured by linear response theory. Ourresults also suggest strategies for more efficiently estimating hydration freeenergies of realistic solutes in bulk water and at interfaces.
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