  Quantum simulations of the hydroxide anion and hydroxyl radical are reported,
employing variational quantum algorithms for near-term quantum devices. The
energy of each species is calculated along the dissociation curve, to obtain
information about the stability of the molecular species being investigated. It
is shown that simulations restricted to valence spaces incorrectly predict the
hydroxyl radical to be more stable than the hydroxide anion. Inclusion of
dynamical electron correlation from non-valence orbitals is demonstrated,
through the integration of the variational quantum eigensolver and quantum
subspace expansion methods in the workflow of N-electron valence perturbation
theory, and shown to correctly predict the hydroxide anion to be more stable
than the hydroxyl radical, provided that basis sets with diffuse orbitals are
also employed. Finally, we calculate the electron affinity of the hydroxyl
radical using an aug-cc-pVQZ basis on IBM's quantum devices.
