Beyond the one-body Green's function: Multichannel Dyson equations for photoemission spectra

We present the multichannel Dyson equation [1,2] (MCDE), which couples two or more independent-particle n-body Green’s functions through a multichannel self-energy.

In particular, the method couples a 1-body Green’s function with a 3-body Green’s function to simulate photoelectron spectroscopy. Conventional Dyson equation approaches typically start from the 1-body Green’s function and include satellite excitations through a complicated dynamical 1-body self-energy. In contrast, the MCDE incorporates correlation effects already at the independent-particle level, allowing for a static multichannel self-energy.

The MCDE is exact up to 2nd order in the interaction and includes many higher-order diagrams to describe screening and other correlation effects. This formalism overcomes key shortcomings of standard approaches such as GW, which suffers from self-screening and fails to reproduce the satellites in the spectral function of the Hubbard dimer. The MCDE is exact for the standard Hubbard dimer[2] and yields very accurate results for H2–like models[3].

Here, we present photoemission spectral functions of small molecules obtained with the MCDE.