We employed density
functional theory-based ab initio molecular
dynamics simulations to examine the hydration structure of several
common alkali and alkali earth metal cations. We found that the commonly
used atom pairwise dispersion correction scheme D3, which assigns
dispersion coefficients based on the neutral form of the atom rather
than its actual oxidation state, leads to inaccuracies in the hydration
structures of these cations. We evaluated this effect for lithium,
sodium, potassium, and calcium and found that the inaccuracies are
particularly pronounced for sodium and potassium compared to the experiment.
To remedy this issue, we propose disabling the D3 correction specifically
for all cation-including pairs, which leads to a much better agreement
with experimental data.