You can find the article from the Arxiv.

Usually one assumes that because of the fast stratification on top of the neutron star all of the heavy elements sink to the bottom of the atmosphere leaving us with pure hydrogen (or helium) composition. Strong convection can, however, cause this assumption to break as it can mix the photosphere thoroughly. To find out how do these kinds of atmospheres emit, we computed a set of detailed state-of-the-art atmosphere models.