Can coupled-cluster theory treat conical intersections?

Andreas Köhn, A. Tajti

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Conical intersections between electronic states are of great importance for the understanding of radiationless ultrafast relaxation processes. In particular, accidental degeneracies of hypersurfaces, i.e., between states of the same symmetry, become increasingly relevant for larger molecular systems. Coupled-cluster theory, including both single and multireference based schemes, offers a size-extensive description of the electronic wave function, but it sacrifices the Hermitian character of the theory. In this contribution, we examine the consequences of anti-Hermitian contributions to the coupling matrix element between near-degenerate states such as linear dependent eigenvectors and complex eigenvalues. Numerical examples are given for conical intersections between two excited states calculated at the equation-of-motion coupled-cluster level which indeed show the predicted artifacts. A simple method is suggested which allows physically meaningful potential energy surfaces to be extracted from the otherwise ill-behaved results. This provides a perspective for obtaining potential energy surfaces near conical intersections at the coupled-cluster level.

Original languageEnglish
Article number044105
JournalThe Journal of Chemical Physics
Volume127
Issue number4
DOIs
Publication statusPublished - 2007

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intersections
Potential energy surfaces
potential energy
Electronic states
Relaxation processes
Wave functions
electronics
Excited states
Eigenvalues and eigenfunctions
Equations of motion
artifacts
eigenvectors
equations of motion
eigenvalues
wave functions
symmetry
matrices
excitation

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Can coupled-cluster theory treat conical intersections? / Köhn, Andreas; Tajti, A.

In: The Journal of Chemical Physics, Vol. 127, No. 4, 044105, 2007.

Research output: Contribution to journalArticle

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