Algebraic Diagrammatic Construction Theory of Charged Excitations With Consistent Treatment of Spin-Orbit Coupling and Dynamic Correlation

TL;DR

This paper develops algebraic diagrammatic construction (ADC) methods to accurately simulate charged excitations, incorporating spin-orbit coupling and dynamic correlation for both single- and multireference wavefunctions, applicable to atoms and small molecules.

Contribution

It introduces a unified ADC framework that includes spin-orbit effects and supports both Hartree-Fock and multiconfigurational references, with benchmarking demonstrating its accuracy.

Findings

SR-ADC is competitive with MR-ADC when multireference effects are negligible.

MR-ADC provides more reliable results for multiconfigurational states.

Spin-orbit ADC methods effectively interpret modern spectroscopic data.

Abstract

We present algebraic diagrammatic construction theory for simulating spin-orbit coupling and electron correlation in charged electronic states and photoelectron spectra. Our implementation supports Hartree-Fock and multiconfigurational reference wavefunctions, enabling efficient correlated calculations of relativistic effects using single-reference (SR-) and multireference (MR-) ADC. We combine the SR- and MR-ADC methods with three flavors of spin-orbit two-component Hamiltonians and benchmark their performance for a variety of atoms and small molecules. When multireference effects are not important, the SR-ADC approximations are competitive in accuracy to MR-ADC, often showing closer agreement with experimental results. However, for electronic states with multiconfigurational character and in non-equilibrium regions of potential energy surfaces, the MR-ADC methods are more reliable, predicting accurate excitation energies and zero-field splittings. Our results demonstrate that the spin-orbit ADC methods are promising approaches for interpreting and predicting the results of modern spectroscopies.