An Introduction to Coupled Cluster Diagrams

For example, we denote the one-electron component of the Hamiltonian, by a dashed interaction line capped by an X. This operator may be 

Ppor an explanation of -creation and -annihilation operators, see the earlier discussion of the particle-hole formalism in the section on The Fermi Vacuum and Particle-Hole Formalism. 

The cluster operator diagrams are particularly simple to interpret as matrix elements the diagrams always involve the reference determinant on the right (because they contain no lines below the interaction line) and an excited determinant on the left, for example, 

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