Energy-specific Bethe-Salpeter equation implementation for efficient optical spectrum calculations.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Accurate calculation of optical spectra is crucial for understanding electronic properties.
• Traditional methods struggle with high-lying excitation energies and large systems.
• The GW-Bethe-Salpeter equation (GW-BSE) formalism is powerful but computationally demanding.

Purpose of the Study:

• To present an efficient energy-specific Bethe-Salpeter equation (BSE) implementation.
• To enable accurate calculation of core and valence optical spectra for large systems.
• To improve the computational efficiency of high-energy excited state investigations.

Main Methods:

• Developed an energy-specific Bethe-Salpeter equation (BSE) approach.
• Utilized the Davidson algorithm with subspace expansion for targeted excitation energies.
• Applied the method to multiple energy windows, ensuring orthogonal trial vectors for accelerated convergence.
• Combined with G0W0 calculations starting from hybrid PBEh solutions.

Main Results:

• Achieved small errors (~0.8 eV) for K-edge excitation energies in small molecules.
• Demonstrated computational efficiency by simulating N 1s K-edge spectrum of porphine.
• Successfully calculated valence optical spectra of silicon nanoclusters with 6000 excited states.

Conclusions:

• The energy-specific BSE method significantly enhances the applicability of GW-BSE formalism.
• This approach is effective for investigating high-energy excited states in large and complex systems.
• Opens new avenues for accurate electronic structure calculations in various fields.