How to Compute Isomerization Energies of Organic Molecules with Quantum Chemical Methods

ArticleinThe Journal of Organic Chemistry 72(6):2118-26 · March 2007with15 Reads
DOI: 10.1021/jo062446p · Source: PubMed
The reaction energies for 34 typical organic isomerizations including oxygen and nitrogen heteroatoms are investigated with modern quantum chemical methods that have the perspective of also being applicable to large systems. The experimental reaction enthalpies are corrected for vibrational and thermal effects, and the thus derived "experimental" reaction energies are compared to corresponding theoretical data. A series of standard AO basis sets in combination with second-order perturbation theory (MP2, SCS-MP2), conventional density functionals (e.g., PBE, TPSS, B3-LYP, MPW1K, BMK), and new perturbative functionals (B2-PLYP, mPW2-PLYP) are tested. In three cases, obvious errors of the experimental values could be detected, and accurate coupled-cluster [CCSD(T)] reference values have been used instead. It is found that only triple-zeta quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work. Augmentation of small basis sets with diffuse functions has a notable effect in B3-LYP calculations that is attributed to intramolecular basis set superposition error and covers basic deficiencies of the functional. The new methods based on perturbation theory (SCS-MP2, X2-PLYP) are found to be clearly superior to many other approaches; that is, they provide mean absolute deviations of less than 1.2 kcal mol-1 and only a few (<10%) outliers. The best performance in the group of conventional functionals is found for the highly parametrized BMK hybrid meta-GGA. Contrary to accepted opinion, hybrid density functionals offer no real advantage over simple GGAs. For reasonably large AO basis sets, results of poor quality are obtained with the popular B3-LYP functional that cannot be recommended for thermochemical applications in organic chemistry. The results of this study are complementary to often used benchmarks based on atomization energies and should guide chemists in their search for accurate and efficient computational thermochemistry methods.
    • "[11][12][13][14][15][16][17][18][19] The problems are especially acute for isomerization enthalpies of environmentally relevant compounds derived from the fuel processing industry, where some DFT and semiempirical methods exhibit severe errors. [20][21][22][23]In previous work, we demonstrated that the perhydro-and perfluoro-alkane derivative branching errors in gas phase standard state (298.15 K, 1 atm) isomerization enthalpies (D isom H (g) ) for the popular B3LYP density functional do not become clear until chain lengths of 5 to 6 carbons and higher. "
    [Show abstract] [Hide abstract] ABSTRACT: The gas phase standard state (298.15 K, 1 atm) isomerization enthalpy (ΔisomH°(g)) prediction performance of the major semiempirical, ab initio, and density functional levels of theory for environmentally relevant transformations was investigated using the linear to branched heptanes as a representative case study. The M062X density functional, MP2 (and higher) levels of Moller-Plesset perturbation theory, and the CBS and Gaussian-n composite methods are well suited for investigating the thermodynamic properties of environmentally interesting isomerizations, although the M062X functional may not be appropriate for all systems. Where large molecular systems prohibit the use of higher levels of theory, the PM6 and PDDG semiempirical methods may offer an appropriate computational cost-accuracy compromise.
    Full-text · Article · Mar 2016
    • "predicting thermochemical parameters for molecular systems with noncovalent interactions9101112131415161718192021. For this reason, we used some of the DFT methods recently developed, such as Thrular's M06L (reported to have the best overall performance of any functional for the study of organometallic thermochemistry22232425262728), the hybrid meta-GGA BMK functional which was reported to be superior to B3LYP and other hybrid functionals for equilibrium properties2930313233 as well as the ωB97XD functional that includes dispersion corrections. Further, G2 and G3 methods, which provide the most accurate predictions of thermochemical parameters , have also been implemented for comparison. "
    [Show abstract] [Hide abstract] ABSTRACT: Experimental mass-spectrometry data on thermochemistry of methide transfer reactions (CH3)3M(+) + M'(CH3)4 ↔ M(CH3)4 + (CH3)3M'(+) (M, M' = Si, Ge or Sn) and the formation energy of the [(CH3)3Si-CH3-Si(CH3)3](+) complex are used as benchmarks for DFT methods (B3LYP, BMK, M06L, and ωB97XD). G2 and G3 theory methods are also used for the prediction of thermochemical data. BMK, M06L, and ωB97XD methods give the best fit to experimental data (close to chemical accuracy) as well as to G2 and G3 results, while B3LYP demonstrates poor performance. From the first three methods M06L gives the best overall result. Structures and formation energies of intermediate "mixed" [(CH3)3M-CH3- M'(CH3)3] complexes not observed in experiment are predicted. Their structures, better described as M(CH3)4∙[M'(CH3)3](+) complexes, explain their fast decompositions.
    Full-text · Article · Nov 2013
    • "Evaluation of the performance of density functionals (DFs) by benchmarking for different realistic chemical tasks is a crucial step prior to the investigation of new problems. Several sets were developed in recent years to test DFs, such as atomization energies,6–8 noncovalent interactions,9–12 and thermochemistry and kinetics.13–15 Many of these were collected in the GMTKN3016 test set by our group to build a large benchmark, which includes a thorough treatment of the chemically important main-group chemistry. "
    [Show abstract] [Hide abstract] ABSTRACT: The performance of 23 density functionals, including one LDA, four GGAs, three meta-GGAs, three hybrid GGAs, eight hybrid meta-GGAs, and ten double-hybrid functionals, was investigated for the computation of activation energies of various covalent main-group single bonds by four catalysts: Pd, PdCl(-), PdCl2, and Ni (all in the singlet state). A reactant complex, the barrier, and reaction energy were considered, leading to 164 energy data points for statistical analysis. Extended Gaussian AO basis sets were used in all calculations. The best functional for the complete benchmark set relative to estimated CCSD(T)/CBS reference data is PBE0-D3, with an MAD value of 1.1 kcal mol(-1) followed by PW6B95-D3, the double hybrid PWPB95-D3, and B3LYP-D3 (1.9 kcal mol(-1) each). The other tested hybrid meta-GGAs perform less well (M06-HF: 7.0 kcal mol(-1); M06-2X: 6.3 kcal mol(-1); M06: 4.9 kcal mol(-1)) for the investigated reactions. In the Ni case, some double hybrids show larger errors due to partial breakdown of the perturbative treatment for the correlation energy in cases with difficult electronic structures (partial multi-reference character). Only double hybrids either with very low amounts of perturbative correlation (e.g., PBE0-DH) or that use the opposite-spin correlation component only (e.g., PWPB95) seem to be more robust. We also investigated the effect of the D3 dispersion correction. While the barriers are not affected by this correction, significant and mostly positive results were observed for reaction energies. Furthermore, six very recently proposed double-hybrid functionals were analyzed regarding the influence of the amount of Fock exchange as well as the type of perturbative correlation treatment. According to these results, double hybrids with <50-60 % of exact exchange and ∼30 % perturbative correlation perform best.
    Full-text · Article · Jun 2013
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