Quantitative Computational Thermochemistry of Transition Metal Species

Abstract

The correlation consistent Composite Approach (ccCA), which has been shown to achieve chemical accuracy ((1 kcal mol -1 ) for a large benchmark set of main group and s-block metal compounds, is used to compute enthalpies of formation for a set of 17 3d transition metal species. The training set includes a variety of metals, ligands, and bonding types. Using the correlation consistent basis sets for the 3d transition metals, we find that gas-phase enthalpies of formation can be efficiently calculated for inorganic and organometallic molecules with ccCA. However, until the reliability of gas-phase transition metal thermochemistry is improved, both experimentally and theoretically, a large experimental training set where uncertainties are near (1 kcal mol -1 (akin to commonly used main group benchmarking sets) remains an ambitious goal. For now, an average deviation of (3 kcal mol -1 appears to be the initial goal of "chemical accuracy" for ab initio transition metal model chemistries. The ccCA is also compared to a more robust but relatively expensive composite approach primarily utilizing large basis set coupled cluster computations. For a smaller training set of eight molecules, ccCA has a mean absolute deviation (MAD) of 3.4 kcal mol -1 versus the large basis set coupled-clusterbased model chemistry, which has a MAD of 3.1 kcal mol -1 . However, the agreement for transition metal complexes is more system dependent than observed in previous benchmark studies of composite methods and main group compounds.

Activation of Carbon−Hydrogen and Hydrogen−Hydrogen Bonds by Copper−Nitrenes: A Comparison of Density Functional Theory with Single- and Multireference Correlation Consistent Composite Approaches

“…[39][40][41][42][43] Hence, the ccCA approach was employed in this study to compare with results obtained from DFT methods. Classical activation barriers as predicted by ccCA 42 were in much better agreement than G3B as compared to very high accuracy computed values obtained from the Truhlar et al databases.…”

Density functional localized orbital corrections for transition metals

“…But a recent study with a small data set using similar CCSD͑T͒ protocol gave a MAD value for transition metals of 3.1 kcal/ mol. 96 We obtained a value of 51.5 kcal/ mol for the D 0 for ScCH 3 . This result is, as suggested above, much closer to the B3LYP-LOC result ͑47.1 kcal/ mol͒ than to the experimental result ͑32.8 kcal/ mol͒, confirming the original hypothesis that the latter is substantially in error.…”

Highly energetic nitrogen species: Reliable energetics via the correlation consistent Composite Approach (ccCA)

“…The method has been successful in the prediction of energetic properties, even where other composite approaches have had difficulties (e.g., s-block [27]) or may be undeveloped or in their infancy (e.g., for transition metal species [25,28]). The ccCA utilizes the correlation consistent basis sets [29,30] which are extrapolated to the CBS limit and MP2 calculations to obtain a reference energy upon which the composite method is based.…”