Cannot find lennard jone parameter

Dear LAMMPS Experts,

I’m trying to simulate a system with a crystallized FeCO3 structure. The problem is I cannot find the corresponding lennard-jones parameters. Where could I find it?

Thanks in advance

a) you are posting to the wrong forum category. If you want to ask LAMMPS experts you have to pick one of the LAMMPS categories. I am taking the liberty to move the topic there.
b) your question is assuming that LJ is a potential suitable for modeling your system. I seriously doubt that.

At any rate, the place to find suitable force fields and potential parameters is the published literature. You need to find studies of the same system and look up what people used for those. If those publications are properly done (and properly reviewed) then it will contain all necessary information either directly or citations of the corresponding publications.