  We introduce an approach to improve single-reference coupled cluster theory
in settings where the Aufbau determinant is absent from or plays only a small
role in the true wave function. Using a de-excitation operator that can be
efficiently hidden within a similarity transform, we create a coupled cluster
wave function in which de-excitations work to suppress the Aufbau determinant
and produce wave functions dominated by other determinants. Thanks to an
invertible and fully exponential form, the approach is systematically
improvable, size consistent, size extensive, and, interestingly, size intensive
in a granular way that should make the adoption of some ground state techniques
such as local correlation relatively straightforward. In this initial study, we
apply the general formalism to create a state-specific method for
orbital-relaxed singly excited states. We find that this approach matches the
accuracy of similar-cost equation-of-motion methods in valence excitations
while offering improved accuracy for charge transfer states. We also find the
approach to be more accurate than excited-state-specific perturbation theory in
both types of states.
