Targeting doubly-excited states with Equation of Motion Coupled Cluster theory restricted to double excitations

Abstract

The accurate description of doubly-excited states using conventional electronic structure methods is remarkably challenging, primarily because such excited states require the inclusion of doubly or higher excited configurations or the application of multi-reference methods. We present a new approach to target electronically excited states that feature a double-electron transfer. Our method uses the equation of motion (EOM) formalism with a pair coupled cluster doubles (pCCD) reference function, where dynamical correlation is accounted for by a linearized coupled cluster correction with singles and doubles (LCCSD). Specifically, our proposed EOM-pCCD-LCCSD model represents a simplification of the conventional EOM-CCSD approach, where the electron-pair amplitudes of CCSD are tailored by pCCD. The performance of EOM-pCCD-LCCSD is assessed for the lowest-lying excited states in CH${}^{+}$ and all-trans polyenes. In contrast to conventional EOM-CC methods with at most double excitations, EOM-pCCD-LCCSD predicts the right order of states in polyenes with excitation energies closest to experiment, outperforming even highly-accurate methods such as the density matrix renormalization group algorithm.

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References in corpus (2)

• Projected seniority-two orbital optimization of the Antisymmetric Product of one-reference orbital Geminal
• Targeting excited states in all-trans polyenes with electron-pair states

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