I want to calculate effective interaction between two charged molecules in aqueous solution. The simulation system include two molecules(including 50 LJ atoms, respectively), 3000 water(LJ liquid),and counterions( 100 anion). There are mainly three interactions in my system, U_LJ(Lennard Jones potential) and U_coulomb (Coulomb potential), and U_FENE bond.
Firstly, the pair of molecules are placed symmetrically along the body diagonal of the cubic simulation box ( I used fix spring command with tether keyword in LAMMPS). The distance R of two molecules acts as a parameter and could be varied.
Next, I want to calculate the effective force F_i acting on each molecule i (i = 1,2) . The force F_i( i = 1,2) would be due to the other molecule, solution and counterions. How Can I calculate the force F_i with LAMMPS command or how can I dump all pair force as data for postprocessing when running LAMMPS in code?
Any sugesstions is highly appreciated.