Dear all,

I hope you are having a good day.

I am writing to inquire about potential errors in calculating the interaction energy between cations and anions in a system composed of a polymer chain and ionic liquids at varying weight percentages (60%, 70%, 75%, 100%). Typically, the absolute value of the interaction energy should increase with the percentage of ionic liquid, but our calculations show otherwise: about 8,000 at 100%, 20,000 at 60%, 35,000 at 70%, and 49,000 at 75%, which suggests an anomaly at 100%.

This issue was raised by a client and is supported by figures in the attached paper, which show an increase in the absolute value of interaction energy between EMIM and FSI as the concentration approaches 100%.

It seems that the error may have occurred during the process of calculating interaction energy after removing the polymer chain. To address this, I intend to use the pair-wise interaction energy method in LAMMPS, where group1 is assigned to the polymer, group2 to the cation, and group3 to the anion. The entire system remains intact while only the interaction energies between groups 2 and 3 are calculated.

Previously, I was informed that a script could resolve this issue. I would appreciate any guidance on how to implement this method in the script.

Additionally, I received the following query regarding the translation of interaction energy values from kcal/mol to a per-particle basis: "If you do an NPT on the n% ionic system I would expect to get the same average energy per the number of anion/cation pairs (o.k depending some deviation of size effects)."

Thank you for your attention to this matter.

Best regards,
Rakhoon Choi