Targeting excited states in all-trans polyenes with electron-pair states

Abstract

Wavefunctions restricted to electron pair states are promising models for strongly-correlated systems. Specifically, the pair Coupled Cluster Doubles (pCCD) ansatz allows us to accurately describe bond dissociation processes and heavy-element containing compounds with multiple quasi-degenerate single-particle states. Here, we extend the pCCD method to model excited states using the equation of motion (EOM) formalism. As the cluster operator of pCCD is restricted to electron-pair excitations, EOM-pCCD allows us to target excited electron-pair states only. To model singly excited states within EOM-pCCD, we modify the configuration interaction ansatz of EOM-pCCD to contain also single excitations. Our proposed model represents a simple and cost-effective alternative to conventional EOM-CC methods to study singly excited electronic states. The performance of the excited state models is assessed against the lowest-lying excited states of the uranyl cation and the two lowest-lying excited states of all-trans polyenes. Our numerical results suggest that EOM-pCCD including single excitations is a good starting point to target singly excited states.

4 figures

References in corpus (4)

• Entanglement Measures for Single- and Multi-Reference Correlation Effects
• Quasiparticle Coupled Cluster Theory for Pairing Interactions
• Projected seniority-two orbital optimization of the Antisymmetric Product of one-reference orbital Geminal
• Analysis of two-orbital correlations in wavefunctions restricted to electron-pair states

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