Fragment-Based Excited-State Calculations Using the GW Approximation and the Bethe-Salpeter Equation

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Calculating excited states of molecular systems is crucial for understanding photophysical and photochemical processes.
• Accurate methods for excited-state calculations are computationally expensive for large systems.

Purpose of the Study:

• To develop an efficient and accurate fragment-based approach for calculating charged and neutral excited states in molecular systems.
• To enable large-scale calculations of delocalized excited states in molecular aggregates.

Main Methods:

• Fragment-based approach utilizing the many-body Green's function method within the GW approximation and Bethe-Salpeter equation (BSE).
• Implementation based on the many-body expansion of total irreducible polarizability using fragment molecular orbitals.
• Large-scale GW/BSE method incorporating the fragment molecular orbital method and exciton model for molecular aggregates.

Main Results:

• Fragment-based GW/BSE methods accurately reproduce results from unfragmented calculations with errors below 100 meV.
• Accuracy of total irreducible polarizability is systematically improved by including two-body correction terms.
• The proposed approach demonstrates efficiency for excited-state calculations in large molecular systems.

Conclusions:

• The fragment-based GW/BSE approach provides a computationally efficient and accurate method for excited-state calculations.
• This method is suitable for studying large molecular systems and aggregates, advancing the understanding of their electronic properties.