Increasing the applicability of DFT I: Non-variational correlation corrections from Hartree–Fock DFT for predicting transition states

Hartree–Fock DFT (HF-DFT) uses the self-interaction error free HF density and DFT functional. Using HF-DFT for molecular structure determination requires a non-variational analytical gradient scheme. This has been developed and applied for the calculation of transition state geometries and barrier heights for chemical reactions. The barrier heights obtained show average absolute errors (AAE) of 2–3 kcal/mol while Λ CCSD(T) show an AAE of 1.1–1.4 kcal/mol. Standard variational DFT with the same functional has AAE’s of 6.3–8.3 kcal/mol while the HF errors are about 12 kcal/mol.