Despite of its importance in understanding the pearlitic transformation, the atomic structures and orientation relationships (ORs) of the ferrite/cementite interface (FCI) have not been revealed. Combining atomic simulation and atomically informed Frank-Bilby theory, we characterize the interface formation energy and detailed information of interface dislocations. We analyzed three traditionally reported ORs (Bagaryatsky, Isaichev, and Pitsch-Petch), and two recently found ORs (Near Bagaryatsky and Near Pitsch-Petch) using a recently developed Fe-C MEAM potential (L.S.I. Liyanage et al., Phys. Rev. B, (2014). 89.). Our results show that the interface formation energies of Bagaryatsky and Pitsch-Petch ORs are significantly higher than those of Isaichev, Near Bagaryatsky and Near Pitsch-Petch ORs, due to higher self-energies of interface dislocations. Our finding supports experimental results (Y.D. Zhang et al., J. Appl. Cryst., (2007). 40.) which exclude the existence of Bagaryatsky and Pitsch-Petch ORs based on accurate crystallographic measurements.