  Density functional theory (DFT) provides convenient electronic structure
methods for the study of molecular systems and materials. Regular Kohn-Sham DFT
calculations rely on unitary transformations to determine the ground-state
electronic density, ground state energy, and related properties. However, for
dissociation of molecular systems into open-shell fragments, due to the
self-interaction error present in a large number of density functional
approximations, the self-consistent procedure based on the this type of
transformation gives rise to the well-known charge delocalization problem. To
avoid this issue, we showed previously that the cluster operator of
coupled-cluster theory can be utilized within the context of DFT to solve in an
alternative and approximate fashion the ground-state self-consistent problem.
This work further examines the application of the singles cluster operator to
molecular ground state calculations. Two approximations are derived and
explored: i), A linearized scheme of the quadratic equation used to determine
the cluster amplitudes, and, ii), the effect of carrying the calculations in a
non-self-consistent field fashion. These approaches are found to be capable of
improving the energy and density of the system and are quite stable in either
case. The theoretical framework discussed in this work could be used to
describe, with an added flexibility, quantum systems that display challenging
features and require expanded theoretical methods.
