  We study many-body correlations in the ground states of a general quantum
system of bosons or fermions by including an additional Jastrow function in our
ecently proposed variational coupled-cluster method. Our approach combines the
dvantages of state-dependent correlations in the coupled-cluster theory and of
strong, short-ranged correlations of the Jastrow function. We apply a
generalized linked-cluster expansion for the Jastrow wavefunction and provide
detailed analysis for practical evaluation of Hamiltonian expectation value as
an energy functional of the Jastrow function and the bare density-distribution
functions introduced and calculated in our earlier publications; a simple,
first-order energy functional is derived and detailed formulas for higher-order
contributions are provided. Our energy functional does not suffer the
divergence as in most coupled-cluster calculations when applying to
Hamiltonians with hardcore potentials. We also discuss relations between our
energy functional and the energy functionals from other theories.
