Occupation deficiency in layered structures of UNi$_{x}$Sb$_2$ ($ 0 \leq x \leq 1 $) studied by density functional theory supercell calculations

Abstract

The five crystal structures of selected UNi$_{x}$Sb$_2$ compositions are investigated by density functional theory supercell calculations. The considered phases are USb$_2$, UNi$_{0.33}$Sb$_2$, UNi$_{0.5}$Sb$_2$, UNi$_{0.66}$Sb$_2$, and UNiSb$_2$ ($x$ = 0, 1/3, 1/2, 2/3, 1). The occupation deficiency of Ni is modeled by removing the Ni layers from constructed supercells, followed by relaxation of the structures. A linear dependence of the lattice parameter $c$ versus Ni concentration $x$ is observed, same, fulfilling the empirical Vegard's law. The agreement between results of our calculations with the empirical data from literature confirms the validity of our approach of supercells with empty Ni layers, at least in predicting of lattice parameters. The calculated with orbital polarization magnetic moments on uranium atoms decrease from 1.70 $\mu_{\mathrm{B}}$ to 1.61 $\mu_{\mathrm{B}}$ with increasing Ni concentration $x$. In comparison to available empirical data of USb$_2$ and UNi$_{0.5}$Sb$_2$, the magnetic moments calculated with orbital polarization are less than 10% smaller.