Use of Löwdin orthogonalised Fermi orbitals for self-interaction corrections in an iron porphyrin

Abstract

ABSTRACTA new approach for formulating the self-interaction correction, referred to as the Fermi-Löwdin orbital-based self-interaction correction (FLO-SIC), is briefly reviewed and applied to the Fe(II)-porphyrin molecule. The Fermi–Löwdin orbitals are localised but due to the fact they are constructed directly from the spin-density matrices, they lead to a set of orbitals that have the property that each and every orbital is explicitly invariant to unitary transformations. These orbitals allow one to constrain the Perdew–Zunger self-interaction correction in a manner that ensures that the energy is explicitly invariant to unitary transformations and size-extensive. We review these improvements and show how the multiple solutions, intrinsic to the original formulation, are removed through the constraint offered by the Fermi–Löwdin construction. The locations of descriptors of Fermi–Löwdin orbital imitate the formation of classical chemical bonds. The very first application of this method to a system containing a transition metal atom is presented here.