De-perturbative corrections for charge-stabilized double ionization potential equation-of-motion coupled-cluster method

Abstract

Charge stabilization improves the numeric performance of double ionization potential equation-of-motion (EOM-DIP) method when using unstable (autoionizing) dianion references. However, the stabilization potential introduces an undesirable perturbation to the target states' energies. Here we introduce and benchmark two approaches for removing the perturbation caused by the stabilization. The benchmark calculations of excitation energies in selected diradicals illustrate that the so-called core correction based on evaluating the perturbation in a small basis set is robust and yields reliable EOM-DIP values, i.e., the errors of 0.0-0.3 eV against a similar-level coupled-cluster approach.

Spin-orbit couplings within the equation-of-motion coupled-cluster framework: Theory, implementation, and benchmark calculations

“…51 Some extensions of EOM-CC (such as the spin-flip and double ionization potential methods) facilitate the treatment of multi-configurational wave functions that appear, for example, in bond breaking and polyradicals. 57,[60][61][62][63][64][65][66][67][68][69] The EOM-CC methods are closely related, or in some situations equivalent, to the linear-response CC approaches. [70][71][72][73][74] The EOM-CC wave function has the following form:…”

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

“…By using complex scaling and complex absorbing potential techniques, we extended these powerful methods to describe autoionising states, such as transient anions, highly excited electronic states, and core-ionised species [183][184][185]. In addition, users can employ stabilisation techniques using charged sphere and scaled atomic charges options [186]. Various improvements of iterative diagonalisation algorithms enable access to high-lying interior eigenvalues.…”

EOM-CC guide to Fock-space travel: the C2 edition

“…This is similar to metastable radical monoanions where the extra electron is trapped behind an angularmomentum barrier also affording resonance character. In a computational treatment using a sufficiently large basis, the wave function of a resonance becomes more and more diffuse, approximating a continuum state corresponding to an electron-detached system and a free electron [70][71][72] .…”

“…The easiest and most commonly used one is to use a relatively small basis set, such that the reference state is artificially stabilized 50,60,61,64-66,76 . Kuś and Krylov have investigated an alternative strategy, stabilization of the resonance using an artificial Coulomb potential with a subsequent de-perturbative correction 71,72 . Here we show that in the case of C 2 using the aug-cc-pVTZ basis provides a robust description of the dianionic reference, delivering accurate results for the target states.…”