Simulating X-ray Photoelectron Spectra With Strong Electron Correlation Using Multireference Algebraic Diagrammatic Construction Theory

TL;DR

This paper introduces a computationally efficient multireference approach combining ADC theory and core-valence separation to accurately simulate X-ray photoelectron spectra of strongly correlated molecules, outperforming traditional methods.

Contribution

The paper develops CVS-MR-ADC, a novel method that effectively models core ionization in strongly correlated systems with low computational cost.

Findings

CVS-MR-ADC matches single-reference ADC accuracy for weakly correlated molecules.

It provides more accurate results for multireference systems like stretched nitrogen and ozone.

Multireference effects are crucial for correctly describing core-hole screening in XPS spectra.

Abstract

We present a new theoretical approach for the simulations of X-ray photoelectron spectra of strongly correlated molecular systems that combines multireference algebraic diagrammatic construction theory (MR-ADC) [J. Chem. Phys., 2018, 149, 204113] with core-valence separation (CVS) technique. The resulting CVS-MR-ADC approach has a low computational cost while overcoming many challenges of the conventional multireference theories associated with the calculations of excitations from inner-shell and core molecular orbitals. Our results demonstrate that the CVS-MR-ADC methods are as accurate as single-reference ADC approximations for predicting core ionization energies of weakly-correlated molecules, but are more accurate and reliable for systems with multireference character, such as stretched nitrogen molecule, ozone, and isomers of benzyne diradical. We also highlight the importance of multireference effects for the description of core-hole screening that determines the relative spacing and order of peaks in the XPS spectra of strongly correlated systems.