Discrepancies between opal and OP opacities at high densities and temperatures

Recent comparisons between OPAL and OP Rosseland mean opacities show general good agreement, although there are some differences. In particular, the largest discrpancies are found at high temperatures and densities relevant to the solar interior. It is shown that certain photo-absorption cross-sections were excluded from the OP atomic data which can contribute to the opacity at these extreme conditions. It is also shown that OP makes approximations in the implementation of their occupation probability formalism that reduces the number of electrons in excited bound states. Calculations suggest that these factors could explain most of the difference at high temperatures and densities.