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Density functional theory (DFT) provides convenient electronic structuremethods for the study of molecular systems and materials. Regular Kohn-Sham DFTcalculations rely on unitary transformations to determine the ground-stateelectronic density, ground state energy, and related properties. However, fordissociation of molecular systems into open-shell fragments, due to theself-interaction error present in a large number of density functionalapproximations, the self-consistent procedure based on the this type oftransformation gives rise to the well-known charge delocalization problem. Toavoid this issue, we showed previously that the cluster operator ofcoupled-cluster theory can be utilized within the context of DFT to solve in analternative and approximate fashion the ground-state self-consistent problem.This work further examines the application of the singles cluster operator tomolecular ground state calculations. Two approximations are derived andexplored: i), A linearized scheme of the quadratic equation used to determinethe cluster amplitudes, and, ii), the effect of carrying the calculations in anon-self-consistent field fashion. These approaches are found to be capable ofimproving the energy and density of the system and are quite stable in eithercase. The theoretical framework discussed in this work could be used todescribe, with an added flexibility, quantum systems that display challengingfeatures and require expanded theoretical methods.

Cluster Amplitudes and Their Interplay with Self-Consistency in Density Functional Methods