Calculation of interaction energy between small molecules

GROMACS version: 2018.3
GROMACS modification: No
My system contains 512 ion pairs of Choline Chloride, 1024 EG, and 170 paracetamol molecules. I have calculated SR LJ and Coulomb energy between different energy groups. The SR LJ+Coul energy for different pairs are as follows:

  1. -12000 kJ/mol for paracetamol-paracetamol
  2. -17800 kJ/mol for choline chloride-paracetamol
  3. -88800 kJ/mol for choline chloride-EG
  4. -10300 kJ/mol for EG-paracetamol

Are these values physically possible? I have often found much less energy values in literature. Am I missing something?

Thanks in Advance
Dhrubajyoti Maji

This could be reasonable numbers. But interaction energies are nearly meaningless for most purposes. I don’t know what literature values you are referring to, but most relative interaction free-energies are usually what matters. So there contain energy differences, not absolute interaction energies and also contain entropic contributions.

Many thanks for your reply. Some papers report this summation of sort range Coulomb and LJ energies as ‘interaction energy’. They studied the variation of this IE across temperature or composition. Here I’m trying to calculate the same by changing the number of paracetamol molecules. But the reported values are in the range of 300 kJ/mol whereas for my system values are too high. This is where confusion arises.

I don’t believe such approaches are useful.
But isn’t the issue simply that you get the sum over all molecules, where the literature value is per molecule? (whatever that might mean, the results would still depend on concentration)

Dear Mr. Dhrubajyoti,

I was interested in your MD simulation.
I am also trying MD simulation of the Choline chloride and Ethylene glycol system.
But, I am having trouble with that.
Could you give some advices on that, please?
My email is:
I would really appreciate your help.