Beyond Quasi-Particle Self-Consistent GW for Molecules with Vertex Corrections

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• The Green's function (GW) approximation is a standard for calculating electronic properties.
• Accurate prediction of charged excitations like electron affinities remains challenging.
• The Bethe-Salpeter equation (BSE) is used to describe two-particle properties.

Purpose of the Study:

• Introduce and evaluate the qsΣ^BSE@L^BSE method for electronic self-energy calculations.
• Assess the impact of including vertex corrections in both the two-particle response function (L) and the self-energy (Σ).
• Improve the description of electron affinities and fundamental gaps in organic molecules.

Main Methods:

• Implemented the qsΣ^BSE@L^BSE approach within the quasi-particle self-consistent GW (qsGW) framework.
• Calculated the two-particle response function (L) by solving the Bethe-Salpeter equation with a static, first-order GW kernel.
• Incorporated the same kernel directly into the self-energy (Σ).

Main Results:

• The qsΣ^BSE@L^BSE method significantly improves electron affinity predictions compared to methods that only include vertex corrections in L.
• This approach maintains the accuracy of qsGW for ionization potentials and fundamental gaps.
• Performance for neutral charge-transfer excitations was comparable to existing BSE@qsGW methods.

Conclusions:

• qsΣ^BSE@L^BSE is a promising approximation for electronic self-energy beyond the standard GW approximation.
• Including vertex corrections in both L and Σ is crucial for accurate charged excitation energies.
• Future work should explore dynamical vertex effects and higher-order corrections for further accuracy improvements.