Electronic structure of the Np$MT_{5}$ ($M$ = Fe, Co, Ni; $T$ = Ga, In) series of neptunium compounds

Evolution of the electronic structure of the Np$M$Ga$_{5}$ ($M$ = Fe, Co, Ni) series of neptunium compounds, whose crystal structure is similar to that of the known family of Pu115 superconductors, was studied by the LDA + $U$ + SO method. The calculations took into account both the strong electron correlations and the spin–orbit coupling in the 5$f$ shell of neptunium. For the first time, the electronic structure was calculated for a hypothetical series of compounds in which gallium is replaced with indium. Parameters of the crystal structure of the given series were obtained using the relationship between the parameters of the crystal structure of the earlier-studied compounds PuCoGa$_{5}$ and PuCoIn$_{5}$. The analysis of the electronic structure and characteristics of neptunium ions calculated in the framework of the LDA + $U$ + SO method showed that the neptunium ions in Np$M$In$_{5}$ with $M$ = Fe, Co, and Ni should have an electron configuration closer to $f^4$, but a spin and magnetic characteristics close to those in Np$M$Ga$_{5}$.