  We present a mean field theory for excited states that is broadly analogous
to ground state Hartree-Fock theory. Like Hartree-Fock, our approach is
deterministic, state-specific, applies a variational principle to a minimally
correlated ansatz, produces energy stationary points, relaxes the orbital
basis, has a Fock-build cost-scaling, and can serve as the foundation for
correlation methods such as perturbation theory and coupled cluster theory. To
emphasize this last point, we pair our mean field approach with an excited
state analogue of second order Moller-Plesset theory and demonstrate that in
water, formaldehyde, neon, and stretched lithium fluoride, the resulting
accuracy far exceeds that of configuration interaction singles and rivals that
of equation of motion coupled cluster.
