Theoretical investigation on electronic and mechanical properties of ternary actinide (U, Np, Pu) nitrides

Abstract

Actinide mononitrides as a promising advanced nuclear fuel have recently earned much attention. We herein studied the electronic and mechanical properties of the ternary actinide mixed mononitrides A0.5B0.5 N (A, B = U, Np, and Pu) using the density functional theory +U method. It is found that in the studied ternary mixed mononitrides, the 5f electronic states of all actinide atoms maintain the local electronic character and do not overlap with each other. Compared with their corresponding binary mononitrides, the U-N bond becomes more ionic, where the Np-N and Pu-N bonds become more covalent in ternary actinide mixed mononitrides. The mechanical properties (such as bulk and shear moduli, Young's modulus, and Poisson's ratio) of three ternary actinide (U-Pu) mononitrides are found to be similar to that of their corresponding binary actinide mononitrides and thus are expected not to misbehave with actinide mononitrides in respect of mechanics. In addition, all the three ternary actinide mononitrides have no imaginary frequencies in their vibration curves and correspondingly satisfy the stability criteria for elastic constants of tetragonal structures.

Exploring Optical and Vibrational Properties of the Uranium Carbonate Andersonite with Spectroscopy and First-Principles Calculations

“…The strong on-site Coulomb interaction of localized f electrons of uranium is not correctly described in DFT by the local density approximation or by the generalized gradient approximation (GGA) but can be implemented with an additional Hubbard-like term U . This DFT + U method has been applied to actinides and UO 2 . − However, proper choices of U energy should be made for f orbitals. Calculations can be also computationally prohibitive for large systems and may converge to metastable states .…”

Ab initio study of dynamical properties of U–Nb alloy melt*

“…More advanced methods, such as DFT + U, are required to properly model the electronic and magnetic properties of uranium compounds, such as UO 2 [25] and UN. [26] However, there is no consensus on whether DFT+U method is necessary to correctly describe U metal and its alloys. Meanwhile, previous studies have suggested that conventional DFT is sufficient for U, [27] UZr alloys, [28] and UAl system.…”