How To Arrive at Accurate Benchmark Values for Transition Metal Compounds: Computation or Experiment?

Abstract

With the objective of analyzing which kind of reference data is appropriate for benchmarking quantum chemical approaches for transition metal compounds, we present the following, (a) a collection of 60 transition metal diatomic molecules for which experimentally derived dissociation energies, equilibrium distances, and harmonic vibrational frequencies are known and (b) a composite computational approach based on coupled-cluster theory with basis set extrapolation, inclusion of core-valence correlation, and corrections for relativistic and multireference effects. The latter correction was obtained from internally contracted multireference coupled-cluster (icMRCC) theory. This composite approach has been used to obtain the dissociation energies and spectroscopic constants for the 60 molecules in our data set. In accordance with previous studies on a subset of molecules, we find that multireference corrections are rather small in many cases and CCSD(T) can provide accurate reference values, if the complete basis set limit is explored. In addition, the multireference correction improves the results in cases where CCSD(T) is not a good approximation. For a few cases, however, strong deviations from experiment persist, which cannot be explained by the remaining error in the computational approach. We suggest that these experimentally derived values require careful revision. This also shows that reliable reference values for benchmarking approximate computational methods are not always easily accessible via experiment and accurate computations may provide an alternative way to access them. In order to assess how the choice of reference data affects benchmark studies, we tested 10 DFT functionals for the molecules in the present data set against experimental and calculated reference values. Despite the differences between these two sets of reference values, we found that the ranking of the relative performance of the DFT functionals is nearly independent of the chosen reference.

On Achieving High Accuracy in Quantum Chemical Calculations of 3d Transition Metal-Containing Systems: A Comparison of Auxiliary-Field Quantum Monte Carlo with Coupled Cluster, Density Functional Theory, and Experiment for Diatomic Molecules

“…We compare the MR-CCSD(T) and CCSD(T) values reported in Ref. 7 to the reference values, and find that the CC methods display a number of large outliers (fewer for the MR-corrected version). We also analyze the performance of 10 DFT functionals, reported in Ref.…”

Predicting Ligand-Dissociation Energies of 3d Coordination Complexes with Auxiliary-Field Quantum Monte Carlo

“…[31][32][33][34][35] However, the reliability of CC methods for transition metal systems, even when multireference effects are approximated, has been the subject of vigorous debate, as illustrated by recent studies on transition metal diatomic-ligand systems. 24,[36][37][38][39][40][41] de Oliveira-Filho and co-workers found that even multireference CCSD(T) could not predict the bond dissociation energies (BDEs) for some diatomics accurately with respect to experimental measurements. A recent study by Head-Gordon and co-workers found that high levels of CC, up to CCSDTQ, are required for chemical accuracy against an exact method known as Adaptive Sampling Configuration Interaction (ASCI) results, albeit in a small basis set.…”

Performance of Density Functional Theory for Transition Metal Oxygen Bonds

“…For small systems, accurate quantum‐chemical methods can compute the energies of bond formation and bond breaking, which enables a test of the accuracy of DFT methods used for specific systems. In particular, the use of the BDEs of metal‐ligand bonds are receiving significant attention as best‐practice benchmark properties for chemical reactivity across the d‐block . The success largely relates to the fact that the diatomic M−O BDEs correlate better than any other known single descriptor to the chemisorption energies of pure metal surfaces, with R 2 approaching 0.89 when computed with the same methods, across a range of more than 500 kJ/mol in both O 2 chemisorption energies and M−O BDEs within the d‐block.…”

“…In particular, the use of the BDEs of metalligand bonds are receiving significant attention as best-practice benchmark properties for chemical reactivity across the dblock. [30,[33][34][35][36][37][38][39][40] The success largely relates to the fact that the diatomic MÀ O BDEs correlate better than any other known single descriptor to the chemisorption energies of pure metal surfaces, with R 2 approaching 0.89 when computed with the same methods, [30] across a range of more than 500 kJ/mol in both O 2 chemisorption energies and MÀ O BDEs within the dblock. Coordinative saturation, metalÀ metal modulations and solvent effects contribute smaller errors to the DFT-modelled process than the local MÀ O bond, because the relative MÀ O bond energies vary by an order of magnitude more than the metalÀ metal modulating influences, or correspondingly, the trend in cohesive energy changes upon ligand dissociation from different metal surfaces.…”