Density functional theory (DFT) suffers from self-interaction errors (SIE) that generally result in the underestimation of chemical reaction barrier heights. This is commonly attributed to delocalization of electrons over stretched bonds found in transition state structures. The Perdew-Zunger self-interaction correction (PZSIC) and locally scaled self-interaction correction (LSIC) improve the barrier heights for many reactions, with LSIC giving better accuracy than PZSIC on average. These methods employ an orbital-by-orbital correction scheme to remove the one-electron SIE using Fermi-Löwdin orbitals (FLOs).<br/> <br/>The self-interaction correction (SIC) can be divided into a term due to the changes in the density when SIE is removed (density-driven errors) and a term due to energy corrections from each of the FLOs.  In many cases the density-driven error is small.  We hypothesize that the SIC contribution to the reaction barrier comes mainly from a limited number of orbitals that are directly involved in bond-breaking and bond-making in the reaction transition state. We call these participant orbitals (PO), in contrast to spectator orbitals (SO) that are not directly involved in changes to the bonding. <br/> <br/>We test this hypothesis by examining the reaction barriers for the BH76 dataset. We find that it is generally followed when the overall SIC contribution to the reaction barrier is large; however, it does not hold in all cases for either PZSIC or LSIC. While the POs contribute more to the correction of the barriers on a per orbital basis, there are many cases where the total SIC contribution from the SOs is significant and cannot be ignored.

Assessing self-interaction correction from active fermi-Löwdin orbitals in FLOSIC

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