Symmetry breaking and self-interaction correction in the chromium atom and dimer

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Density functional approximations (DFAs) are crucial for studying electron correlation.
• Strongly correlated systems, like the chromium dimer, present challenges for DFAs.
• Symmetry-breaking is a key mechanism for DFAs to describe these systems.

Purpose of the Study:

• To investigate the effects of self-interaction correction (SIC) on the chromium dimer.
• To evaluate the accuracy of a full Perdew-Zunger SIC applied to the local spin density approximation (LSDA).
• To understand the implications of unphysical symmetry-breaking in electronic structure calculations.

Main Methods:

• Utilized density functional approximations, specifically LSDA and PBE-GGA.
• Applied a full Perdew-Zunger self-interaction correction (SIC) to LSDA.
• Analyzed the binding energy curve and electronic configuration of the chromium dimer and isolated chromium atom.

Main Results:

• LSDA and PBE-GGA qualitatively and quantitatively describe the chromium dimer's binding curve with antiferromagnetic symmetry-breaking.
• A full Perdew-Zunger SIC to LSDA results in an unphysical symmetry-broken state, significantly lowering the total energy.
• This unphysical state exhibits zero magnetic moment but non-zero atomic spin density, and the dimer's energy exceeds that of separated atoms.

Conclusions:

• Full SIC to LSDA overcorrects for the chromium dimer, leading to unphysical electronic states.
• The findings suggest that SIC methods may require scaling down in regions with significant electron correlation.
• This work provides qualitative evidence for refining SIC implementations in electronic structure theory.