Off-Diagonal Self-Energy Terms and Partially Self-Consistency in GW Calculations for Single Molecules: Efficient...

Area of Science:

• Computational Physics
• Quantum Chemistry
• Materials Science

Background:

• Density Functional Theory (DFT) struggles with accurate prediction of electronic excitation energies.
• Approximate exchange-correlation (XC) functionals in DFT introduce artifacts.
• Kohn-Sham (KS) single-particle energies and states are common inputs for advanced methods.

Purpose of the Study:

• To develop an efficient approximation scheme for the GW method.
• To improve the accuracy of single-particle excitation energies beyond bare KS estimates.
• To reduce fundamental shortcomings of DFT in calculating excitation energies.

Main Methods:

• The study employs the GW method, utilizing Kohn-Sham energies and states.
• A novel approximation scheme is proposed for the quasi-particle (qp) equation.
• The scheme is based on second-order perturbation theory and self-consistent iterations.

Main Results:

• The proposed GW approximation significantly improves single-particle excitation energy predictions.
• The method effectively reduces artifacts from approximate XC functionals.
• The approach avoids solving large eigenvalue problems, offering computational efficiency.

Conclusions:

• The efficient GW approximation provides accurate excitation energies comparable to the GW truncation uncertainty.
• This method offers a computationally tractable way to overcome DFT limitations for electronic excitations.
• The scheme yields corrected excitation energies and quasi-particle wave functions.