Constructing "Full-Frequency" Spectra via Moment Constraints for Coupled Cluster Green's Functions

Area of Science:

• Quantum chemistry
• Condensed matter physics
• Computational materials science

Background:

• Calculating quasiparticle spectra is crucial for understanding material properties.
• Traditional methods like Green's function approaches can be computationally expensive.
• Accurate spectral representations are needed across all energy scales.

Purpose of the Study:

• To develop an efficient and systematically improvable method for computing full-frequency quasiparticle spectra.
• To leverage static expectation values for spectral moment constraints.
• To reduce the computational cost compared to existing Green's function techniques.

Main Methods:

• Utilizing conserved static expectation values to define spectral distribution moments.
• Employing an expansion based on these moments for spectral reconstruction.
• Computing moment constraints at the coupled-cluster (CC) level.
• Testing the approach on the GW100 benchmark set for charged excitation spectra.

Main Results:

• Demonstrated convergence of correlated state-specific and full spectral quantities.
• Achieved a fraction of the computational effort compared to traditional Green's function methods.
• Successfully converged frontier excitations to the accuracy of the coupled-cluster singles and doubles (CCSD) approximation.
• Obtained a simultaneous representation of the entire excitation spectrum.

Conclusions:

• The proposed method offers an efficient pathway to full-frequency quasiparticle spectra.
• It provides accurate results for frontier excitations and the complete spectrum.
• This approach presents a significant advancement in computational spectroscopy.