Stationary coupled-cluster approaches to molecular properties: a comparative study

Abstract

We show in this paper that the use of an extended coupled-cluster functional leads to a more desirable stationary-response formulation for molecular properties than that obtained by the use of an expectation-value functional. We make a detailed formal and numerical analysis of relative suitability of both the functionals. In particular, we investigate the extent of size-separation error using a truncated expectation-value functional and examine the relative accuracy and convergence of the two functionals in extracting molecular properties. We have also compared the results obtained by the use of these two functionals with the nonvariational coupled-cluster results.