  Classical novae are significant sources of interstellar material, especially
carbon, nitrogen and oxygen. These standard candles are only behind supernovae
and $\gamma$-ray bursts as the third brightest objects in the sky, and the most
probable progenitors of type Ia supernovae.
  After a nova outburst the system enters into the constant bolometric
luminosity phase and the nova maintains a stable hydrogen burning in the
surface layers of the white dwarf. As the expanding shell around the nova
attenuates, progressively deeper and hotter layers become visible. At the end
of the constant bolometric luminosity phase, the hottest layers are exposed and
novae radiate X-rays.
  This work uses the static, plane-parallel model atmosphere code TLUSTY to
calculate atmospheric structure and SYNSPEC to calculate synthetic X-ray
spectra. It was necessary to incorporate atomic data for the highest ionization
stages of elements ranging from hydrogen to iron in both programs. Atomic data
on energy levels, bound-free, bound-bound transitions and natural broadening
were taken from NIST and TOPbase.
  Extensive tests revealed the importance of line opacities on atmospheric
parameters and on the final spectra. A correlation can be defined between
effective temperature and surface gravity. The spectral appearance is not very
sensitive to the joint changes of both. Due to this effect both parameters
might be over-estimated with static models. These tests also showed that N VI
and N VII lines are good indicators of the effective temperature.
  Model fitting of V4743 Sgr and V2491 Cyg confirmed the anticipated impact of
modeling geometry and stellar wind. The ionization balance and line profiles
indicate that both novae are close to or over the Eddington limit. These
results are consistent with previous studies; further and unambiguous details
require a comprehensive update of TLUSTY, what is under way.
