oa Benchmark study of density functional methods for organometallic reactions

Reactions involving the formation of new metal-ligand bonds are particularly important in the energy industry as most catalytic processes involves the use of organometallic complexes as the catalyst. Using computational methods it is now possible to predict pathways and energy barriers for various catalytic reactions. We can easily predict whether a reaction is feasible or not without having to perform experiments. However, the main limitation of computational approaches is that they are highly dependent on the method that is chosen. Density functional theory (DFT) has become the preferred method for calculating a variety of molecular properties such as thermochemistry and thermochemical kinetics but, there is no universally accepted DFT functional which can be used for these types of studies. The aim of the present study is to find the best suited functional(s) for calculations involving the enthalpy of formations of organometallic complexes. We present a database of enthalpy of formation (ΔH) for 23 organometallic complexes using 26 different density functional methods and studied the accuracy of each DFT functional with respect to the experimental ΔH value. We find the most accurate functional is M06 with a mean unsigned error (MUE) of 1.9 kcal/mol, followed closely by WB97XD, M06L, PBEPBE, PW91PW91 and TPSSTPSS (MUE = 2.0, 2.0, 2.0, 2.1 and 2.3 kcal/mol respectively). The widely accepted traditional functional B3LYP shows very poor performance with a MUE value of 8.6 kcal/mol.