Assessing How Correlated Molecular Orbital Calculations Can Perform versus Kohn–Sham DFT: Barrier Heights/Isomerizations

• Published in: Chemistry : a European journal 2017-07, Vol.23 (38), p.9122-9129
• Main Authors: Varandas, António J. C., Martínez González, Marco, Montero‐Cabrera, Luis A., Garcia de la Vega, José M.
• Format: Article
• Language: English
• Subjects: ab initio calculations; Chemistry; computational chemistry; Correlation; density functional calculations; Density functional theory; Extrapolation; Hydrogen; hydrogen transfer; Isomerization; Mathematical analysis; Organic chemistry; Parameter estimation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201700928

To assess the title issue, 38 hydrogen transfer barrier heights and 38 non‐hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered, in addition to 4 2 p‐isomerization reactions and 6 others for large organic molecules. All Kohn–Sham DFT calculations have employed the popular M06‐2X functional, whereas the correlated molecular orbital (MO)‐based ones are from single‐reference MP2 and CCSD(T) methods. They have all utilized the same basis sets, with raw MO energies subsequently extrapolated to the complete basis set limit without additional cost. MP2 calculations are found to be as cost‐effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data. Although the focus is on barrier heights, the results may bear broader implications, in that one may see successes and difficulties of DFT when compared with traditional MO theories for the same data. Counting the cost: To assess different computational methods, 38 hydrogen transfer barrier heights and 38 non‐hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered. MP2 calculations are as cost‐effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data (see figure).