arXiv subjects

Stefano Paggi

Publications and source records attributed to Stefano Paggi.

4 recordsLinked to original sources

arXiv2026

Benchmark of Multi-Channel Dyson Equation and Algebraic Diagrammatic Construction Methods for molecules

The Dyson-algebraic diagrammatic construction (ADC) and the multi-channel Dyson equation (MCDE) formalisms explicitly leverage multi-particle channels to formulate correlated theories of the single-particle Green's function that produce positive semi-definite spectral functions by construction. While the MCDE is strictly rooted in the Dyson formalism, most ADC calculations are performed in the non-Dyson (nD) framework that decouples electron attachment and detachment sectors. We benchmark the Dyson-ADC(2)-X [that is equivalent to the (3,1)-MCDE] and ADC(3) approximations on a set of 58 ionization potentials of 23 small molecules for which near-full configuration interaction reference data exist. Comparison of Dyson- to nD-ADC(3) reveals deviations of the order of 0.1 eV between both methods, calling into question the reliability of the nD approximation. We show that Dyson-ADC gives similar accuracy for first IPs as for semi-valence and semi-core transitions. Finally, we also benchmark the screened (3,1)-MCDE that screens all ladder interactions, and show that it improves over its unscreened counterpart.

physics.chem-ph↗

arXiv2026

Core and valence photoemission spectra of atoms and molecules from a multichannel Dyson equation

We recently presented multichannel Dyson equations for the \textit{ab initio} simulation of various spectroscopies. In particular, we introduced a multichannel Dyson equation for the description of photoemission spectra. In this work, we apply our approach to the simulation of photoemission spectra of atoms and molecules. We introduce a numerically efficient approach to calculate their spectral functions. We compare the spectra obtained within the multichannel Dyson equation to those obtained with full configuration interaction and the $GW$ method. We are thus able to show that the satellite features due to shake-up processes are significantly better described by the multichannel Dyson equation than by $GW$. Finally, we also discuss the slow convergence of the satellite energies with the size of the basis set and we propose a simple extrapolation method to reach the complete basis-set limit.

cond-mat.other↗

arXiv2025

Ground and excited-state properties of the extended Hubbard dimer from the multichannel Dyson equation

We have recently presented the multichannel Dyson equation as an alternative to the standard single-channel Dyson equation. While the latter involves a single many-body Green's function, the former uses a multichannel Green's function in which two or more many-body Green's functions are coupled. Quasiparticles and satellites are thus naturally treated on equal footing in the multichannel Dyson equation. To assess the accuracy of our approach we apply it here to the ground- and excited-state properties of the extended Hubbard dimer, an exactly solvable model for $H_2$. In particular, we focus on the potential energy surface as well as the corresponding spectral functions and HOMO-LUMO gaps, which are well-known challenges for many-body approximations such as second Born and $GW$. We show that the multichannel Dyson equation gives overall very good results for all properties considered and outperforms both $GW$ and second Born. In particular, the multichannel Dyson equation yields the correct ground-state energy and HOMO-LUMO gap in the dissociation limit contrary to $GW$.

cond-mat.str-el↗

arXiv2025

Multichannel Dyson equations for even- and odd-order Green's functions: application to double excitations

We extend the concept of the multichannel Dyson equation that we have recently derived to model photoemission spectra by coupling the one- and the three-body Green's functions, to higher-order Green's functions and to other spectroscopies. We show the general structure of the equations and how one can systematically approximate the corresponding multichannel self-energy. As a particular case, we focus on the coupling of the two-body and the four-body Green's functions in the electron-hole channel to describe neutral excitations. This formulation allows for the description of important many-body effects, such biexcitons, in a natural way. We illustrate our approach by applying it to a two-level model system, which, in a one-particle picture, exhibits single and double excitations. Our method can correctly describe both kinds of excitation, unlike standard approaches, and in good agreement with the exact results.

cond-mat.str-el↗