LAUSR

Abstract We investigated the electronic heat capacity and energetics of thermal excitations of electrons around Fermi energy of selected metallic compounds (UN, UAl2 and ThN) using first-principles methods. The effect of magnetism was evaluated for UN and UAl2. The generalized gradient approximation (GGA) of the Perdew, Burke, and Ernzerhof functional, developed for solids (/PBEsol) as implemented in Quantum ESPRESSO (QE) was used for UN and UAl2 while the earlier PBE was used for ThN. We found that electrons' thermal excitations would only slightly affect the equilibrium lattice constants in considered compounds except for non-magnetic UN, where it needs to be taken into account. The electron density of states at Fermi energy is larger and therefore an increased effect was found. The calculated electronic heat capacity i predicted to be the largest for non-magnetic UN and very small for non-magnetic ThN. The electronic heat capacity is lower for ferromagnetic UN and UAl2 and larger for all compounds in a non-magnetic state when the lattice constant decreases. Electronic heat capacity increases with temperature and becomes more significant at higher temperatures. The predicted γ coefficients are smaller than the evaluated experimentally at low temperatures, but is in a better agreement with the lower values evaluated at 300 K–1700 K temperature range. Our evaluations of the respective electronic energy correction parameters due to electrons’ thermal excitations show that except for non-magnetic UN, they are at least one order of magnitude smaller than the Gruneisen parameter for ferromagnetic UN, both non-magnetic and ferromagnetic UAl2 and ThN.