Performance of the VBSCF method for pericyclic and π bond shift reactions.

The performance of the valence bond self-consistent field (VBSCF) method was investigated in this paper by predicting the activation barriers and reaction energies in pericyclic and π bond shift reactions for hydrocarbons. The benchmarking set includes 3 electrocyclic reactions, 3 sigmatropic shifts, 3 cycloadditions, 2 cycloreversions, and 7 π bond shift reactions, where the first 11 reactions are taken from Houk's standard set (J. Phys. Chem. A 2003, 107, 11445). Computational results reveal that the VB(CI) method, which performs VBSCF calculations first with full covalent structures and then includes all mono- and di-ionic structures to compute the total energy without further orbital optimization, matches the accuracy of the complete active space SCF (CASSCF) method very well. The mean absolute error values (the deviations from the CASSCF data) are 0.01 kcal/mol for the reaction energy, and 0.26 and 0.32 kcal/mol for the activation energy with the 6-31G and 6-31G(d) basis sets, respectively.