Ab-initio prediction of the phase diagram of thorium

We present density functional theory (DFT) calculations of thorium to predict its solid-solid phase boundaries up to 300 GPa. We first focus on the electronic structure, comparing the predictions of scalar relativistic (SR), scalar relativistic + spin-orbit coupling (SR+SO), and full Dirac solutions at zero temperature, with comparisons to compressive diamond anvil cell experiments. We also look in detail at the computed elastic constants and the orbital contributions to the density of states with increasing pressure through the fcc-bct phase transformation and discuss changes in electronic structure driving the phase transformation. Finally, we investigate the high temperature bcc phase using free energy perturbation theory. While we focus only on solid-solid phase transformations, we will also discuss opportunities for computing the melt curve, which will be the focus of future work.