Cation electric field is related to hydration energy.

Electronic structure calculations on ions that use dielectric continuum theory to mimic solvent around the bare ionic solutes are often prone to make large errors in the hydration energies. It is found for cations that much of the error can be accounted for by a simple linear correlation with the maximum value found anywhere on the dielectric cavity surface of the solute potential or, even better, the outgoing normal electric field, thus mirroring analogous results previously obtained for anions. This correlation allows for significantly improved estimates of cation hydration energies while still retaining cavities of physically reasonable size in determination of the bulk dielectric contributions.