  We study the impact of theoretical uncertainty in the dark matter halo mass
function and halo bias on dark energy constraints from imminent galaxy cluster
surveys. We find that for an optical cluster survey like the Dark Energy
Survey, the accuracy required on the predicted halo mass function to make it an
insignificant source of error on dark energy parameters is ~ 1%. The analogous
requirement on the predicted halo bias is less stringent (~ 5%), particularly
if the observable-mass distribution can be well constrained by other means.
These requirements depend upon survey area but are relatively insensitive to
survey depth. The most stringent requirements are likely to come from a survey
over a significant fraction of the sky that aims to observe clusters down to
relatively low mass, Mth ~ 10^13.7 Msun/h; for such a survey, the mass function
and halo bias must be predicted to accuracies of ~ 0.5% and ~ 1%, respectively.
These accuracies represent a limit on the practical need to calibrate ever more
accurate halo mass and bias functions. We find that improving predictions for
the mass function in the low-redshift and low-mass regimes is the most
effective way to improve dark energy constraints.
