title: 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-cluster-based 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.
authors.affiliation: Center for Advanced Scientific Computing and Modeling (CASCaM), Department of Chemistry, University of North Texas, Denton, Texas 76203, USA.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Deyonker
authors.forename: Kirk A
authors.initials: KA
authors.lastname: Peterson
authors.forename: Gideon
authors.initials: G
authors.lastname: Steyl
authors.forename: Angela K
authors.initials: AK
authors.lastname: Wilson
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Cundari
mesh_terms: D003198:Computer Simulation; D008956:Models, Chemical; D013816:Thermodynamics; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D028561:Transition Elements