The failure of available density functional (DFT) methods to compute accurate electronic structures and energies for complex systems is well documented. In particular, there is often a large variation in the computed energies associated with complex reactions using different popular density functionals. While newly developed dispersion corrected and long-range corrected density functionals offer improved results, the errors are often greater than 5 kcal/mol for many reactions. Moreover, the lack of a universal DFT or a generic protocol to assess DFT errors has compounded the associated problems in quantum chemistry. Herein, we demonstrate that the disparate results from different density functionals stem from the systematic errors in the underlying chemistry representing the elementary changes in the bonding environment between reactants and products. We have developed a rigorous protocol to correct for these systematic errors and obtain dramatically improved results with deviations of only 1–2 kcal/mol for most density functionals. An important characteristic of our protocol is that the corrected results are largely independent of the nature of the underlying density functionals, and approach the accuracy obtained from state-of-the-art coupled cluster methods. The performance of a range of DFT methods for a set of challenging problems – such as pericyclic reactions representing complex electronic rearrangements, bond dissociation energies in large biofuel molecules, or accurate pKa calculations for large drug molecules containing several functional groups – is analyzed and assessed in this work.

Solving the density functional conundrum: Elimination of systematic errors to derive accurate energies for complex chemical reactions

2019 Fall National Meeting

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