I work with a material that is a proton conductor and My MSD calculated for a single acidic proton looks like that (fully scattered) . I use Lammps for the calculations , Calculations are done for a canonical ensemble (NVT) (after equilibrations using both NVT for mixing and NPT for relaxation of any tension etc.) @ 303,15 [K] , timestep = 1 [fs] , Efield = 0,000001 [V/A] , and the proton is held together with a sulfate group just from coulombic interactions (Oxygen of sulfate -1 charge and proton +1 ) . Why is is not diffusing and just stays there attached to the sulfate group ? There is no interaction between sulfate and proton except VDW and Coulomb . Thanks in advance .