  We present a new method for modeling electronically excited states that
overcomes a key failing of linear response theory by allowing the underlying
ground state ansatz to relax in the presence of an excitation. The method is
variational, has a cost similar to ground state variational Monte Carlo, and
admits both open and periodic boundary conditions. We present preliminary
numerical results showing that, when paired with the Jastrow antisymmetric
geminal power ansatz, the variation-after-response formalism delivers
accuracies for valence and charge transfer single excitations on par with
equation of motion coupled cluster, while surpassing even this very high-level
method's accuracy for excitations with significant doubly excited character.
