What is a typical mass density of iron in an neutron star? It is likely to be so dense that nuclei are so close to each other that classical electrostatics might fail, requiring quantum electrodynamics corrections to the Coulomb law describing interaction between point charges assumed in all our calculations. I am not sure nuclei can be seen as point charges in neutron stars, maybe at the surface region.

Formally, one can indeed compress iron in atomistic, DFT calculations to any mass density, provided this does not cause numerical issues due to too close atoms. Also, what do those layered structures look like? I would guess a material under that enormous pressure would show a phase transition to some peculiar phase. In principle, that can be studied, provided the governing equations of DFT still hold true, and no numerical issues are encountered for a given, high mass density.