  A multiconfigurational adiabatic connection (AC) formalism is an attractive
approach to computing dynamic correlation within CASSCF and DMRG models.
Practical realizations of AC have been based on two approximations: i) fixing
one- and two-electron reduced density matrices (1- and 2-RDMs) at the
zero-coupling constant limit and ii) extended random phase approximation
(ERPA). This work investigates the the effect of removing the "fixed-RDM"
approximation in AC. The analysis is carried out for two electronic Hamiltonian
partitionings: the group product function- and the Dyall-Hamiltonians. Exact
reference AC integrands are generated from the DMRG FCI solver. Two AC models
are investigated, employing either exact 1- and 2-RDMs or their second-order
expansions in the coupling constant in the ERPA equations. Calculations for
model molecules indicate that lifting the fixed-RDM approximation is a viable
way toward improving accuracy of the existing AC approximations.
