• DFT;
  • MECP;
  • [FeIVO] unit

In order to test the reliability of DFT methods for calculating electronic structures of [FeIVO] system, detailed calculations of [FeIVO](OH)2 models were performed for several low-energy states using multiconfiguration quasidegenerate perturbation theory (MCQDPT) as well as DFT-based methods. The minimum energy crossing points (MECP) of 5A1/5B2 and 3B2/5B2 were investigated based on Lagrange–Newton approach. The results show that M06 functional produce energy gaps close to those of MCQDPT results. Another topic in this article is that the electron configurations of [FeIVO](OH)2 models strongly depend on the type of surface ligand used, and the two lowest states of these can facile transition each other by the MECP. The practicability of M06 method in locating the MECP is validated by the results of MCQDPT which demonstrate the two-state reactivity (TSR) can be studied with proper DFT method. These inspections provide the basis for further TSR study of larger [FeIVO] system. © 2014 Wiley Periodicals, Inc.