MD simulation on heme structures

I tried to do MD simulation on Hematin molecule (which has a Fe+3) using Forcite and
Discover modules and Compass forcefield in Materials Studio. Doing this I observed that the molecule was deformed unexpectedly, i.e., the Fe went largely out of the molecular plane. I used both Fe+2 and Fe+3 and several hybridization (such as octahedral, square-planar,…) and the result was the same. Is there any solution for this?

I appreciate your answer.