  In this work, we investigate the possibility of improving
multireference-driven coupled cluster (CC) approaches with an algorithm that
iteratively combines complete active space (CAS) calculations with tailored CC
and externally corrected CC. This is accomplished by establishing a feedback
loop between the CC and CAS parts of a calculation through similarity
transformation of the Hamiltonian with those CC amplitudes that are not
encompassed by the active space. We denote this approach the complete active
space iterative coupled cluster (CASiCC) ansatz. We investigate its efficiency
and accuracy in the singles and doubles approximation by studying the
prototypical molecules H4, H8, H2O, and N2. Our results demonstrate that CASiCC
systematically improves on the single-reference CCSD and the ecCCSD methods
across entire potential energy curves, while retaining modest computational
costs. However, the tailored coupled cluster method shows superior performance
in the strong correlation regime suggesting that its accuracy is based on error
compensation. We find that the iterative version of externally corrected and
tailored coupled cluster methods converge to the same results.
