Complex Fermi-Löwdin orbital self-interaction correction

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Density Functional Theory

Background:

• Self-interaction error is a significant issue in standard density functional approximations.
• Fermi-Löwdin self-interaction correction (FLOSIC) is a method to mitigate this error.
• Previous FLOSIC implementations primarily used real orbitals.

Purpose of the Study:

• To introduce and investigate the use of complex Fermi orbital descriptors (FODs) within the FLOSIC framework.
• To compare the results of complex FLO-SIC (cFLOSIC) with real orbital FLOSIC (rFLOSIC) and Perdew-Zunger SIC (PZ-SIC).
• To analyze the impact of complex orbitals on total energies and orbital properties.

Main Methods:

• Implementation of complex Fermi orbital descriptors (FODs) in FLOSIC.
• Performance of complex FLO-SIC (cFLOSIC) calculations using the local spin density approximation.
• Detailed examination of the N2 molecule to analyze differences between real and complex Fermi-Löwdin orbitals (FLOs).

Main Results:

• cFLOSIC calculations generally yield lower total energies compared to rFLOSIC.
• The energy lowering in cFLOSIC is primarily attributed to the exchange-correlation component of the SIC.
• Significant differences between real and complex solutions are observed for highly hybridized atomic orbitals and molecular bonds (e.g., triple bonds in N2).

Conclusions:

• Complex FODs provide a more accurate description within the FLOSIC framework, leading to improved total energies.
• The complex triple-bond orbitals in N2 exhibit a physically intuitive structure.
• The study highlights that FLO centroids are not always optimal for FOD positioning in FLOSIC calculations.