Performance of Density Functional Theory for 3d Transition Metal-Containing Complexes: Utilization of the Correlation Consistent Basis Sets

Calculation of Heats of Formation for Zn Complexes: Comparison of Density Functional Theory, Second Order Perturbation Theory, Coupled-Cluster and Complete Active Space Methods

Heats of formation were predicted for nine ZnX complexes (X= Zn, H, O, F2, S, Cl, Cl2, CH3, (CH3)2) using fourteen density functionals, MP2 calculations and the CCSD and CCSD(T) coupled-cluster methods. Calculations utilized the correlation consistent cc-pVTZ and aug-cc-pVTZ basis sets. Heats of formation were most accurately predicted by the TPSSTPSS and TPSSKCIS density functionals, and the BLYP, B3LYP, MP2, CCSD and CCSD(T) levels were among the poorest performing methods based on accuracy. A wide range of Zn2 equilibrium bond distances were predicted, indicating that many of the studied levels of theory may be unable to adequately describe this transition metal dimer. To further benchmark the accuracy of the density functional methods, high-level CASSCF and CASPT2 calculations were performed to estimate bond dissociation energies, equilibrium bond lengths and heats of formation for the diatomic Zn complexes and the latter two quantities were compared with the results of DFT, MP2 and coupled-cluster calculations as well as experimental values.

A Benchmark Ab Initio and DFT Study of the Structure and Binding of Methane in the σ-Alkane Complex CpRe(CO)2(CH4)

Ab initio molecular orbital theory and density functional theory (DFT) procedures have been used to study the binding of methane in CpRe(CO)2(CH4), the simplest σ-alkane complex in the experimentally widely studied CpRe(CO)2(alkane) family. We find the optimal Re···C, Re···H and C···H distances to be 2.60, 1.92, and 1.15 Å, respectively, on the composite-CCSD(T)/def2-QZVPP (CCSD(T)/def2-TZVP with supplement for the larger def2-QZVPP basis set at the second-order Møller-Plesset perturbation theory level) potential energy surface which has been mapped out at this level of theory. The enthalpy of binding at 298 K was determined to be 62.0 kJ mol(-1) at the composite-CCSD(T)/CBS//B3-PW91/aug-cc-pVTZ-PP level. Benchmarks on the various DFT procedures show that some functionals give good geometries but underestimate binding energies, while others yield poor geometries but give closer agreements with the composite-CCSD(T) binding energy. On the other hand, the ωB97X-D functional gives fair agreements with composite-CCSD(T) for both geometry optimization as well as binding energy. Thus, it appears to be a reliable, easily implemented, and cost-effective means for studying Re-alkane complexes. Good binding energies are also obtained with several common functionals when D3 dispersion corrections are applied. Selected dispersion-corrected DFT methods (B3PW91-D3, TPSSh-D3, and B98-D3) were found to be quite accurate for the calculation of binding energies of several other model metal-CH4 complexes containing a range of metal centers (Rh, Pd, W, Ir, Pt). We also note that, for single-point energy calculation of the Re-CH4 binding, the PWP-B95-D3 double-hybrid DFT procedure provides an excellent agreement with the benchmark energy at only a slightly higher computational requirement.

Comparative Study of Single and Double Hybrid Density Functionals for the Prediction of 3d Transition Metal Thermochemistry

The performance of 13 density functionals, including hybrid-GGA, hybrid-meta-GGA, and double-hybrid functionals, in combination with the correlation consistent basis sets, has been evaluated for the prediction of gas phase enthalpies of formation for a large set of 3d transition-metal-containing molecules with versatile bonding features. Of the methods studied, the hybrid B97-1 functional and the double hybrid functional mPW2-PLYP exhibit the best overall performance with mean absolute deviations (MAD) from experimental data of 7.2 and 7.3 kcal mol(-1), respectively. For single reference molecules, where dynamic correlation predominates, the results of the hybrid functionals B97-1, B98, and ωB97X and the double hybrid functionals B2-PLYP, B2GP-PLYP, and mPW2-PLYP yield the smallest deviations from the experimental enthalpies of formation. For the prediction of thermodynamic properties of coordination complexes including metal carbonyls, B97-1 and mPW2-PLYP are the most promising functionals of those investigated. When the size of the molecule is considered, B97-1 and B98 outperform mPW2-PLYP for diatomics and triatomics, while mPW2-PLYP yields the lowest MAD for larger molecules.

Toward accurate theoretical thermochemistry of first row transition metal complexes

The recently developed correlation consistent Composite Approach for transition metals (ccCA-TM) was utilized to compute the thermochemical properties for a collection of 225 inorganic molecules containing first row (3d) transition metals, ranging from the monohydrides to larger organometallics such as Sc(C(5)H(5))(3) and clusters such as (CrO(3))(3). Ostentatiously large deviations of ccCA-TM predictions stem mainly from aging and unreliable experimental data. For a subset of 70 molecules with reported experimental uncertainties less than or equal to 2.0 kcal mol(-1), regardless of the presence of moderate multireference character in some molecules, ccCA-TM achieves transition metal chemical accuracy of ±3.0 kcal mol(-1) as defined in our earlier work [J. Phys. Chem. A2007, 111, 11269-11277] by giving a mean absolute deviation of 2.90 kcal mol(-1) and a root-mean-square deviation of 3.91 kcal mol(-1). As subsets are constructed with decreasing upper limits of reported experimental uncertainties (5.0, 4.0, 3.0, 2.0, and 1.0 kcal mol(-1)), the ccCA-TM mean absolute deviations were observed to monotonically drop off from 4.35 to 2.37 kcal mol(-1). In contrast, such a trend is missing for DFT methods as exemplified by B3LYP and M06 with mean absolute deviations in the range 12.9-14.1 and 10.5-11.0 kcal mol(-1), respectively. Salient multireference character, as demonstrated by the T(1)/D(1) diagnostics and the weights (C(0)(2)) of leading electron configuration in the complete active self-consistent field wave function, was found in a significant amount of molecules, which can still be accurately described by the single reference ccCA-TM. The ccCA-TM algorithm has been demonstrated as an accurate, robust, and widely applicable model chemistry for 3d transition metal-containing species with versatile bonding features.