Data and code from: The solvation entropy of different simulation models of the hydrated electron

Excess electrons in liquid water, commonly known as hydrated electrons,
have been of great theoretical and experimental interest. Despite this,
there is still no definitive understanding of how the surrounding water
molecules are arranged and fluctuate around the hydrated electron.
Experiments have shown that the hydrated electron has a large positive
solvation entropy, which is quite anomalous among small ions in water,
which usually have negative entropies of solvation. In this work, we use
alchemical simulation, machine learning, and a reference potential
methodology to calculate the solvation entropy of several simulation
models of the hydrated electron, including ab initio molecular
dynamics based on density functional theory (DFT). We find that
cavity-forming one-electron models with relatively soft cavity structures
correctly predict the sign of the hydrated electron’s entropy but
underestimate its magnitude. Both a non-cavity one-electron model and hard
cavity-forming DFT simulations yield a solvation entropy with the
incorrect sign, indicating that the hydration structures predicted by
these methods must be qualitatively incorrect. We rationalize the
calculated solvation entropies of the different hydrated electron models
by examining the structure and dynamic behavior of the first-shell waters.