Assessment of density functional theory in studying on the transition states of a Diiron-mediated N[sbnd]N bond cleavage reaction

Abstract

The structure of transition state is very significant to further understand the related reaction system auxiliary NN bond cleavage process. Here, in order to sort out some DFT functionals in searching the transition states in a NN bond cleavage reaction mediated by the diiron complexes, we compared 49 density functionals with benchmark data of MP2 and DLPNO-CCSD(T) methods. By analyzing the structures and relative energies, we have found two HGGA functionals (B1B95, mPW1PBE) that are more consistently reliable ones. Among them, the B1B95 functional provides the most reliable energetic properties within 8.6 kcal/mol compared with the data of DLPNO-CCSD(T) method. And six HGGA functionals (B1B95, PBE0, mPW1PBE, mPW1PW91, HSEh1PBE, HSE1PBE) and two functionals (B2PLYP-D3, PBE0-D3) with D3 empirical dispersion well optimize the structure of Fe2S2 clusters and evaluate the reaction thermodynamic energy of NN bond cleave process. The functionals with long range correction and D3 empirical dispersion underestimate easily the energy barrier of NN bond cleavage of Fe2S2 clusters.