Simplification of the Fermi–Löwdin Self‐Interaction Correction Method for Efficient Self‐Interaction‐Free Density Functional Calculations

Many failures of density functional approximations are attributed to the self-interaction error. A simplified one-electron self-interaction correction (SIC) scheme is proposed to expedite the SIC calculations. Applications show that for a wide range of properties, it performs similarly to the well-known Perdew–Zunger SIC method at a substantially reduced computational cost.

Fermi–Löwdin orbital self-interaction-correction (FLOSIC) method uses symmetric orthogonalized Fermi orbitals as localized orbitals in one-electron SIC schemes. In FLOSIC, a set of Fermi orbital descriptors (FOD) defines the FLOs and is obtained by energy minimization. Determination of optimal FODs is a computationally very demanding task. Herein, simplification of the FLOSIC calculations by removing self-interaction error from a set of selected orbitals of interest (SOSIC) is proposed. This approach is illustrated by choosing a set of valence orbitals as active orbitals. The results of a wide range of properties obtained using the valence SOSIC (vSOSIC) scheme are compared against the Perdew–Zunger SIC results. The two methods agree within a few percent for the majority of the properties. The mean absolute error in the vertical detachment energy of water cluster anions with vSOSIC-Perdew–Burke–Ernzerhof (PBE) against benchmark CCSD(T) results is only 15 meV making vSOSIC-PBE an excellent alternative to the CCSD(T) for the case. The calculation on the [Cu2$_{2}$Cl6$_{6}$]²⁻ complex demonstrates that the FOD optimization in vSOSIC is substantially smoother and faster. Assessment of the performance of SIC-r2$^{2}$SCAN shows that it performs similarly to the SIC-Strongly Constrained and Appropriately Normed functional (SCAN) for most properties, but for atomization energies, SIC-r2$^{2}$SCAN outperforms SIC-SCAN.

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