Real-Time Coupled-Cluster Approach for the Cumulant Green's Function.

Area of Science:

• Quantum Chemistry
• Many-Body Perturbation Theory
• Spectroscopy

Background:

• Green's function methods are crucial for understanding electronic correlations in excited states.
• Existing cumulant methods are often limited by their linear approximations.

Purpose of the Study:

• To develop a nonlinear, real-time coupled-cluster equation-of-motion approach for the one-electron Green's function.
• To extend previous work on cumulant Green's function methods.

Main Methods:

• Developed a cumulant form of the one-electron Green's function.
• Utilized a real-time coupled-cluster equation-of-motion framework.
• Solved a set of coupled first-order, nonlinear differential equations for the cumulant.

Main Results:

• Obtained a nonperturbative expression for the cumulant.
• Incorporated nonlinear corrections beyond traditional linear self-energy methods.
• Applied the method to core-hole Green's function calculations for small molecules.

Conclusions:

• The nonlinear contributions significantly improve calculations of quasiparticle properties like core-level binding energies.
• The method accurately describes inelastic losses and satellite features in photoemission spectra.
• This approach offers a more robust treatment of electronic correlations in excited-state phenomena.