We show in this paper that the use of an extended coupled-cluster func
tional leads to a more desirable stationary-response formulation for m
olecular properties than that obtained by the use of an expectation-va
lue functional. We make a detailed formal and numerical analysis of re
lative suitability of both the functionals. In particular, we investig
ate 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 c
ompared the results obtained by the use of these two functionals with
the nonvariational coupled-cluster results.