First principles investigation of the electronic-thermal transport of ThN, UN, and ThC

The resistivity and electronic-thermal conductivity of ThN, ThC and UN were compared. It was found that the new electron-phonon physics from first principles code Electron-Phonon coupling using Wannier functions (EPW, v. 5.4) code as implemented in Quantum Espresso (QE, v. 6.8) code based on density-functional theory predicts higher electronic-thermal conductivity for thorium and uranium mononitride than for thorium carbide in agreement with experiment. QE combined with EPW code were used to calculate integrated electron-phonon coupling strength, the Eliashberg transport coupling function, and electron-phonon scattering rates. The electronic resistivity was calculated using Ziman's formula for metals and compared to the values derived from first principles using Boltzmann transport theory. The number of mobility electrons were obtained by equating the calculated resistivity at 1000 K. Estimation showed that in ThN the number of electronic carriers is two times larger and both electron-phonon coupling strength and electron scattering rates are lower, which led to about four times higher electronic thermal conductivity than calculated for ThC. Although a good agreement with experiment was found for ThN and ThC (at high temperatures), the current version of EPW code for non-magnetic solids overestimates the electronic thermal conductivity of UN and underestimates resistivity.