  We use density functional theory within the local density approximation
(LDA), LDA+U, generalized gradient approximation (GGA), GGA+U, and
hybrid-functional methods to calculate the properties of iron monoarsenide.
FeAs, which forms in the MnP structure, is of current interest for potential
spintronic applications as well as being the parent compound for the
newly-identified pnictide superconductors. We compare the calculated
structural, magnetic and electronic properties obtained using the different
functionals to each other and to experiment, and investigate the origin of a
recently-reported magnetic spiral. Our results indicate the appropriateness or
otherwise of the various functionals for describing FeAs and the related
Fe-pnictide superconductors.
