I want to pack 1M C2mim (+) bf4(-) in ACN solution in simulation box of 405800 A^3 I am heavily confused how to decide the no of ion pairs and ACN molecules to pack in the box. Please someone help me out with the way
I bet you want the same number of ions to keep the system charge neutral. You have to work out the concentration (or more simply, the ACN ratio) depending on the system you want to investigate. This information should match reference literature data, experiments, etc.
I was referring a paper. And simulatneously tried to calculate on my own also the values don’t seem to match, the systen is of porous carbon supercapacitor system. The volume I mentioned above is the volume of system including the void voulme in both electrodes. In paper I saw that they are not using the void volume, this is the paper the concentration they have considered is 1.5M Bmim pf6 in ACN but the values I am calculating don’t match. The no of ion pairs is being calculated lesser and the no of ACN molecules are being calculated higher.
I am doing this way:
1)consider density of pure ACN backcalculate the no of molecules for require size of simulation box
2) And considering ion pairs, if 1.5* Avogadro number of ion pairs for 1L then how many ion pairs for required size of simulation box
The no of ion pairs is being calculated lesser and the no of ACN molecules are being calculated higher. They are considering ion pairs 230 while I get 178 and ACN they are using 2146 and my calculation gives me 2270.
This is not a question specific to LAMMPS, but rather for the Science Talk.
It’s hard to work with molar concentrations at the scale of molecular simulations, as the approximation “1 molecule of solvent = 1 molecule of solute” may lead to significant discrepancies. I would rather stick to the molar fraction of each species. If you stick to the numbers provided by the paper you cited, you get 230/(230+2146) = 0.0968. Then you can make a box the size you want and with the number of molecules you want.