  It is generally accepted that the atmospheres of cool/lukewarm stars of
spectral types A and later are described well by LTE model atmospheres, while
the O-type stars require a detailed treatment of NLTE effects. Here model
atmosphere structures, spectral energy distributions and synthetic spectra
computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid
method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE
are compared. Their ability to reproduce observations for effective
temperatures between 15000 and 35000 K are verified. Strengths and weaknesses
of the different approaches are identified. Recommendations are made as to how
to improve the models in order to derive unbiased stellar parameters and
chemical abundances in future applications, with special emphasis on Gaia
science.
