A quick tour of Coupled Cluster theory

The amplutudes \( t \) play a role similar to the coefficients \( C \) in the shell-model calculations. They are obtained by solving a set of non-linear equations similar to those discussed above in connection withe FCI discussion.

If we truncate our equations at the CCSD level, it corresponds to performing a transformation of the Hamiltonian matrix of the following type for a six particle problem (with a two-body Hamiltonian):

\( 0p-0h \) \( 1p-1h \) \( 2p-2h \) \( 3p-3h \) \( 4p-4h \) \( 5p-5h \) \( 6p-6h \)
\( 0p-0h \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) 0 0 0 0
\( 1p-1h \) 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) 0 0 0
\( 2p-2h \) 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) 0 0
\( 3p-3h \) 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) 0
\( 4p-4h \) 0 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \)
\( 5p-5h \) 0 0 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \)
\( 6p-6h \) 0 0 0 0 \( \tilde{x} \) \( \tilde{x} \) \( \tilde{x} \)