A new method for initializing Fermi orbital descriptors for FLO-SIC calculations*

Fermi orbital descriptors (FODs) play a key role in Fermi-Löwdin orbital self-interaction correction (FLO-SIC) calculations used to remove one-electron self-interaction from approximate density functional calculations on an orbital-by-orbital basis. Optimal FODs are obtaining by minimizing the SIC energy, and, in this process, identifying an initial set of FODs becomes crucial for practical applications. Here we propose a novel generator for automatically initializing FODs without requiring much user input based on the minimization of a “pseudo energy” expression that involves a Coulomb electron density attraction, a FOD-FOD short-range repulsion, and an exchange-like density repulsion term. We implemented and tested this method for molecules involving a variety of bonding situations and found that it successfully reproduces FOD configurations that are in qualitative good agreement with Lewis theory. For spin-unpolarized molecules, this method underestimates and overestimates the separation of lone pair FODs in the second- and third-row elements, respectively, while the distances between double and triple bond FODs are slightly exaggerated. For spin-polarized systems, this method can also provide good FODs for radicals and transition states.