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.

中文翻译：

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UN、UAl2和ThN中电子热激发的第一性原理研究

摘要 我们使用第一性原理方法研究了选定金属化合物（UN、UAl2 和 ThN）的费米能附近电子热激发的电子热容和能量学。对 UN 和 UAl2 的磁性影响进行了评估。在 Quantum ESPRESSO (QE) 中实现的 Perdew、Burke 和 Ernzerhof 泛函的广义​​梯度近似 (GGA) 用于固体 (/PBEsol)，用于 UN 和 UAl2，而较早的 PBE 用于 ThN。我们发现电子的热激发只会轻微影响所考虑化合物中的平衡晶格常数，但需要考虑的非磁性 UN 除外。费米能级的电子态密度较大，因此发现效应增加。计算出的电子热容 i 预测非磁性 UN 最大，非磁性 ThN 非常小。当晶格常数降低时，铁磁性 UN 和 UAl2 的电子热容较低，而所有非磁性状态的化合物的电子热容较大。电子热容随温度增加而增加，并且在较高温度下变得更加显着。预测的 γ 系数比在低温下实验评估的要小，但与在 300 K-1700 K 温度范围内评估的较低值更吻合。我们对由电子热激发引起的各个电子能量校正参数的评估表明，除了非磁性 UN，它们至少比铁磁性 UN 的 Gruneisen 参数小一个数量级，