dear all
I’ve been reading so many papers but still i have this problem. i want to model and perform MD simulation on a sphere of fe3o4 but i cant find the potential. i read somewhere that fe3o4 is polar covalent, does it mean that it has bonded terms? i would really appreciate it if someone help me with fe3o4 potential.

There is not much to do here. If you have read so many papers, you should have plenty information about how to model Fe3O4 with classical MD. It is your job to try them out and pick the most suitable for your purpose. It is not the job of the mailing list to do this for your or to spoon feed how to do such a (rather straightforward i might add) task.
Almost anything is “polar covalent”, but whether you need explicit bonds in your input is dependent on the specific model you are using and its requirements for parameter and settings.