Multireference Algebraic Diagrammatic Construction Theory for Excited States: Extended Second-Order Implementation and Benchmark

• Main Authors: Mazin, Ilia M, Sokolov, Alexander Yu
• Format: Journal Article
• Language: English
• Published: 11-09-2021
• Subjects: Physics - Chemical Physics
• DOI: 10.48550/arxiv.2107.04196

J. Chem. Theory Comput. 17, 6152 (2021) We present an implementation and benchmark of new approximations in
multireference algebraic diagrammatic construction theory for simulations of
neutral electronic excitations and UV/Vis spectra of strongly correlated
molecular systems (MR-ADC). Following our work on the first-order MR-ADC
approximation [J. Chem. Phys. 2018, 149, 204113], we report the strict and
extended second-order MR-ADC methods (MR-ADC(2) and MR-ADC(2)-X) that combine
the description of static and dynamic electron correlation in the ground and
excited electronic states without relying on state-averaged reference
wavefunctions. We present an extensive benchmark of the new MR-ADC methods for
excited states in several small molecules, including the carbon dimer,
ethylene, and butadiene. Our results demonstrate that for weakly-correlated
electronic states the MR-ADC(2) and MR-ADC(2)-X methods outperform the
third-order single-reference ADC approximation and are competitive with the
results from equation-of-motion coupled cluster theory. For states with
multireference character, the performance of the MR-ADC methods is similar to
that of an N-electron valence perturbation theory. In contrast to conventional
multireference perturbation theories, the MR-ADC methods have a number of
attractive features, such as a straightforward and efficient calculation of
excited-state properties and a direct access to excitations outside of the
frontier (active) orbitals.