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CONTEXT: For more than two decades, stellar atmosphere codes have been usedto derive the stellar and wind parameters of massive stars. Although they havebecome a powerful tool and sufficiently reproduce the observed spectralappearance, they can hardly be used for more than measuring parameters. Onemajor obstacle is their inconsistency between the calculated radiation fieldand the wind stratification due to the usage of prescribed mass-loss rates andwind-velocity fields. AIMS: We present the concepts for a new generation ofhydrodynamically consistent non-local thermodynamical equilibrium (non-LTE)stellar atmosphere models that allow for detailed studies of radiation-drivenstellar winds. As a first demonstration, this new kind of model is applied to amassive O star. METHODS: Based on earlier works, the PoWR code has beenextended with the option to consistently solve the hydrodynamic equationtogether with the statistical equations and the radiative transfer in order toobtain a hydrodynamically consistent atmosphere stratification. In thesemodels, the whole velocity field is iteratively updated together with anadjustment of the mass-loss rate. RESULTS: The concepts for obtaininghydrodynamically consistent models using a comoving-frame radiative transferare outlined. To provide a useful benchmark, we present a demonstration model,which was motivated to describe the well-studied O4 supergiant Zeta Pup. Theobtained stellar and wind parameters are within the current range of literaturevalues. CONCLUSIONS: For the first time, the PoWR code has been used to obtaina hydrodynamically consistent model for a massive O star. This has beenachieved by a profound revision of earlier concepts used for Wolf-Rayet stars.The velocity field is shaped by various elements contributing to the radiativeacceleration, especially in the outer wind. (...)

Coupling hydrodynamics with comoving frame radiative transfer: I. A unified approach for OB and WR stars