I'm now currently simulating the system in which charged peptide (ARG, LYS, ASP, GLU) is solvated in electrolyte solution. MD simulation was performed based on the AMBER14ffSB force field, but in here I'm not much sure whether this force field accurately models the peptide-ion interaction or not. For instance, trajectory shows a very strong binding between carboxylate ion (C-termini or ASP, GLU side-chain) and sodium ion. I once heard that there are some issues regarding such circumstances, as such some electrostatic interactions are too much overestimated compared to the experimental results. Below is the observed snapshot where blue particles are the sodium ion, coordinated with several carboxylate ions.
Is there any preferred force field in bio-MD community that is known to be superior to other one for capturing such electrostatic interaction? Any recommendation is highly welcomed!