Electronic structure of mononuclear Cu-based molecule from density-functional theory with self-interaction correction

Area of Science:

• Quantum chemistry
• Materials science
• Computational physics

Background:

• Approximate density-functional theory (DFT) functionals suffer from self-interaction error, causing electron and spin density delocalization in 3d orbitals.
• This delocalization inaccurately represents the electronic structure of molecules, particularly those with potential applications in quantum computing.

Purpose of the Study:

• To investigate the electronic structure of a planar mononuclear Cu-based molecule [Cu(C6H4S2)2]z in dianionic (z = -2) and monoanionic (z = -1) states.
• To assess the efficacy of the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method in correcting DFT self-interaction errors for this molecule.
• To evaluate the molecule's potential as a qubit candidate by analyzing its electronic and spin densities.

Main Methods:

• Density-functional theory (DFT) calculations were performed on the Cu-based molecule.
• Fermi-Löwdin orbital self-interaction correction (FLO-SIC) was applied, utilizing a frozen-density loop algorithm.
• Calculations were conducted for two oxidation states: dianionic (z = -2) and monoanionic (z = -1).

Main Results:

• FLO-SIC accurately describes the spin density distribution, showing origin from Cu d and S p orbitals in a 2:1 ratio for the dianionic state, aligning with multireference calculations.
• In contrast, standard DFT reversed this orbital ratio due to self-interaction error.
• FLO-SIC significantly lowers the energy of occupied orbitals, particularly the 3d orbitals, and substantially increases the HOMO-LUMO gap compared to SIC-free DFT.
• The calculated HOMO-LUMO gap for the dianionic state using FLO-SIC is larger than that of the monoanionic state, consistent with experimental observations.

Conclusions:

• The FLO-SIC method provides a more accurate description of the electronic structure of the Cu-based molecule than standard DFT, effectively mitigating self-interaction error.
• The corrected electronic structure and increased energy gap support the potential of this molecule as a qubit candidate.
• FLO-SIC shows promise for accurately describing magnetic exchange coupling in 3d-element-based systems.