  A benchmark study has been carried out on the ground-state potential curve of
the hydroxyl anion, OH^{-}, including detailed calibration of both the
1-particle and n-particle basis sets. The CCSD(T) basis set limit overestimates
$\omega_e$ by about 10 cm^{-1}, which is only remedied by inclusion of
connected quadruple excitations in the coupled cluster expansion --- or,
equivalently, the inclusion of the $2\pi$ orbitals in the active space of a
multireference calculation. Upon inclusion of scalar relativistic effects (-3
cm^{-1} on $\omega_e$), a potential curve of spectroscopic quality (sub-cm^{-1}
accuracy) is obtained. Our best computed EA(OH), 1.828 eV, agrees to three
decimal places with the best available experimental value. Our best computed
dissociation energies, D_0(OH^-)=4.7796 eV and D_0(OH)=4.4124 eV, suggest that
the experimental D_0(OH)=4.392 eV may possibly be about 0.02 eV too low.
