Fermi-Orbital Self-Interaction Correction of Density Functional Theory on Spin-Containing Systems
Open AccessSelf-interaction correction (SIC) is employed to remove the Coulomb interaction between an electron and itself from the approximations of density functional theory (DFT). Without self-interaction corrections or the use of hybrid functionals, approximations to the density-functional theory often favor intermediate spin systems over high-spin systems. Approaches involving empirical parameters, such as Hubbard U, are popular, but the methods preserve the beauty of ab-initio are more preferable. In this dissertation, we investigate the effect of self-interaction corrections to the density functional theory by studying Fe(II)-Porphyrins, which are the molecules responsible for transport oxygen in human body. The inclusion of self-interaction corrections significantly alters the energetic ordering. The recently developed unitarily invariant Fermi-L\"{o}wdin self-interaction corrected method is implemented here. Because the energetics, due to changes in total spin, are small, we have also calculated the second-order spin-orbit energies and the zero-point vibrational energies to determine whether such corrections could be important in the molecular systems, used by nature, for transporting or converting atmospheric chemical constituents. Ourresults find that the size of the spin-orbit and vibrational corrections to the energy orderings are small compared to the changes due to the self-interaction correction. Inclusion of the self-interaction correction, within the Fermi-Orbital formulation introduced by Pederson, Ruzsinszky and Perdew, changes the energetic orderings of the intermediate spin (S=1, two unpaired electrons) and high spin (S=2, four unpaired electrons) states relative to PBE-GGA, and PW92-LDA. Spin dependencies in the infrared/Raman spectra and the zero-field splittings are also provided as a possible means for identifying the spin of Fe(II)-Porphyrins.
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