We use the PHOENIX code package to model the X–ray spectrum of Nova V4743 Sagittarii observed with the LETGS onboard the Chandra satellite on March 2003 .
Our atmosphere models are 1D spherical , expanding , line blanketed , and in full NLTE .
To analyze nova atmospheres and related systems with an underlying nuclear burning envelope at X–ray wavelengths , it was necessary to update the code with new microphysics , as discussed in this paper .
We demonstrate that the X–ray emission is dominated by thermal bremsstrahlung and that the hard X–rays are dominated by Fe and N absorption .
The best fit to the observation is provided at a temperature of T _ { eff } = 5.8 \times 10 ^ { 5 } K , with L _ { bol } = 50 000 L _ { \odot } .
The models are calculated for solar abundances .
It is shown that the models can be used to determine abundances in the nova ejecta .