Natural orbital functional theory and reactivity studies of diradical rearrangements: ethylene torsion as a case study

Abstract

Natural orbital functional theory (NOFT) in its PNOF3 and PNOF4 implementations is used to investigate the potential energy surface (PES) of ethylene torsion. This rearrangement is taken as a case study to illustrate the satisfactory performance of the Piris Natural Orbital Functional (PNOF) toward rearrangements sensible to non-dynamical electron correlation or near-degeneracy effects. We show that the fulfillment of the G-positivity condition, as implemented in PNOF4, is key to yield a correct description of structures with significant diradical character. We have found that PNOF4 yields an accurate description of these delicate PES and predicts the correct trends of the occupation numbers as compared with multiconfigurational wavefunction methods.