Sanibel Symposium

The description of anionic molecules has been problematic within approximations to densityfunctional theory because of self-interaction error, which pushes the eigenvalues to higher energy and creates non-systematic errors in the HOMO/Fermi levels. Fermi-Löwdin orbital-based selfinteraction correction (FLO-SIC) [1], a new approach for improving the Perdew-Zunger selfinteraction correction, is introduced to treat a tri-anionic system. The Fermi–Löwdin orbitals are localized. They are constructed directly from the spin-density matrices, which lead to a set of orbitals with each and every orbital being explicitly unitarily invariant and size-extensive. As such the resulting energies also are unitarily invariant and size-extensive. The improvement of alignment of Fermi level in the system is demonstrated. Through the analysis of the magnetic structure of the tri-anionic molecule, the instability of electronic structure caused by selfinteraction error is revealed.