  In this paper, we present a refined calculation of the atmospheric neutrino
flux spanning from GeV to PeV energies. Our method, Daemonflux, utilizes
data-driven inputs and incorporates adjustable parameters to take their
uncertainties into account. By optimizing these parameters using a combination
of muon data and constraints from fixed-target experiments, we achieve
uncertainties in the calculated neutrino fluxes of less than 10% up to 1 TeV,
with neutrino ratios constrained to below 10%. Our model performs particularly
well at energies below 100 GeV, where the smallest errors are obtained. We make
our model available as a software package that provides access to predictions
of fluxes, ratios, and errors, including the covariance matrix obtained from
the fit.
