Dear Ahmed

###how to get C-C, C-O and C-O atomic interactions from the obtained energy graph###

I think, first u have to calculate C-C, C-O and C-O interaction energy separately. For that first U have separate all the monomers like xxxxxxC and Cxxxxxxx (for C-C) and xxxxxC and Oxxxxx (for C-O), and then calculate energy individually to calculate the interaction energy using equation IE = total energy of complex - (monomer energy1 + monomer2).

#######how to extract LJ parameters########

 Can u insert the potential energy surface graph of CO2 dimer with stretching their bond length then i can help u as per my experience.

Regards,

Nandan 

Dear Ahmed, I can find the temperature dependence for the CO2 dimer bond energy from precise experimental thermophysical data. It would be interestig to compare the Molecular Dynamics estimations with my results.

Regards,

Boris Sedunov

Dear Ahmed, I have done some similar calculations for CO adsorption on catalyst surface (J Chem Phys 145, 084506). However, in my case I only had to evaluate LJ parameters for the binary interactions of carbon-cobalt. In your case, besides LJ parameters of all your binary intermolecular interactions, you may need some angular or dihedral interactions between the two molecules of your dimer. For the intramolecular bond strength and angular interactions you may use an existing forcefield parameters and discuss that the required corrections effect are included in the newly derived LJ parameters.

Alireza