Precise diffusion coefficients for white dwarf astrophysics

Abstract

Observations of Galactic white dwarfs with Gaia have allowed for unprecedented modelling of white dwarf cooling, resolving core crystallization, and sedimentary heating from neutron-rich nuclei. These cooling sequences are sensitive to the diffusion coefficients of nuclei in Coulomb plasmas which have order 10 per cent uncertainty and are often not valid across coupling regimes. Using large-scale molecular dynamics simulations we calculate diffusion coefficients at high resolution in the regime relevant for white dwarf modelling. We present a physically motivated law for diffusion with a semi-empirical correction which is accurate at the percent level. Implemented along with linear mixing in stellar evolution codes, this law should reduce the error from diffusion coefficients by an order of magnitude.