GW-BSE for molecular excited states in REST: State-of-the-art methods, acceleration strategies, and the LAMB...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate prediction of molecular excited states is crucial for understanding photophysical and photochemical processes.
• Existing GW-BSE methods often face computational challenges, limiting their application to larger systems.

Purpose of the Study:

• To present a robust and efficient implementation of the GW-BSE approach for molecular excited states.
• To introduce novel approximations and acceleration strategies to reduce computational cost.
• To provide a reliable tool for excited-state calculations in computational chemistry.

Main Methods:

• Implementation of GW-BSE within a Rust-based electronic structure toolkit.
• Utilized resolution-of-identity and contour deformation techniques.
• Incorporated various GW variants (G0W0, evGW, rsGW) and BSE calculations.
• Introduced the low angular momentum basis approximation for BSE (LAMB-BSE).
• Evaluated three acceleration strategies: GW extrapolation, virtual orbital cutoff, and LAMB-BSE.

Main Results:

• Achieved meV-level agreement with MolGW for quasiparticle and excitation energies.
• Demonstrated that rsGW significantly improves upon G0W0 for HOMO energies (376 meV MAE).
• GW extrapolation reduced calculations by an order of magnitude with <43 meV errors.
• Virtual orbital cutoff yielded a 9x speedup with minimal errors (<10 meV).
• LAMB-BSE provided 1.5x acceleration with <20 meV deviations for singlets and triplets.

Conclusions:

• The REST implementation of GW-BSE offers a computationally efficient and accurate tool for molecular excited-state studies.
• The developed acceleration strategies provide practical guidelines for balancing accuracy and efficiency.
• Public availability of the code and documentation encourages community adoption and further research.