Fine Structure of the Dielectric Response to a Molecular-Sized Ion in Water

We have revisited water polarization phenomena caused by a charge of a solute whose size is the same as water molecules, because there is a qualitative discrepancy in the calculated results between various methods. The polarization was calculated using molecular dynamics (MD) simulations. Various basic cell sizes and charges of the solute were examined. In the case of a positive solute, the dependence of the polarizability on the value of solute charge showed a maximum. However, the response to the solute charge was not saturated, and it approached a linear response behavior. The feature for a negative solute was almost the same, but much more remarkable. Our results show not only a strong nonlinearity of the dielectric response but also fine structure in the polarizability curve. A picture for water polarization is discussed based on the differences between previous results and our results.