All pair coeffs are not set.

LAMMPS LAMMPS Beginners
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Dear LAMMPS users and developers,

I am new to LAMMPS, trying to run MD simulations using PCFF-IFF force field.

My system includes: a platinum slab, a complex of oligomers and drugs dissolved in chloroform (solvent will be changed later), and ions.

LAMMPS (22 Jul 2025 - Update 2)

I used LUNAR and Packmol to make my ‘‘data file’’ for oligomer-drug and the ‘‘molecule template’’ for chloroform solvent. I have built my LAMMPS with Openkim and wanted to try ‘‘Sim_LAMMPS_IFF_PCFF_HeinzMishraLinEmami_2015Ver1v5_FccmetalsMineralsSolventsPolymers__SM_039297821658_001’’. However, I didn’t see any paramters and type for any anions like Cl- to neutrilze the system! Therefore, I am using class2 commands instead. I am a bit confused about the cause of an error when both the kim and class2 commands are used. So any guide would be so appreciated. The input file and log file are attached to this post and can be found below. The error is telling that not all pair coeffs are set. Also, it would be nice if anyone could suggest any easier ways to handle creating molecule template files, atom typing, and create_box.

Sorry if the answer to my question could be found in the documentation or elsewhere, but my progress has been really slow. Any help is greatly appreciated, and any interest in contributing is most welcome.

Thank you all.

Pt_PoAP_CLO_min (2.5 KB)

Pt_PoAP_CLO_v3.log (7.0 KB)

Best regards,

Enayat Mohsenzadeh

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Given your state of affairs, there is little that can be done by an online forum. You need some proper in-person tutoring and learn some LAMMPS basics and force field basics first.

If you have not done so, I suggest you let your current project rest for a few weeks and spend some time with the available LAMMPS tutorials (for example https://dx.doi.org/10.33011/livecoms.6.1.3037) and study some introductory publication (there is a decent review co-authored by the people that developed the force field you mentioned at: https://doi.org/10.1021/acs.jpcb.3c08419 https://doi.org/10.26434/chemrxiv-2024-zdf3l).
The important steps are that you don’t rush and don’t progress until you are satisfied with your level of understanding and verified it by talking to somebody with experience.

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