Structural, elastic, electronic and thermodynamic investigations of neptunium chalcogenides: First-principles calculations

Theoretical study of structural, elastic, electronic and thermodynamic properties of neptunium chalcogenides NpX (X = S, Se, Te) in NaCl-B1 and CsCl-B2 phases are investigated using the first principles calculations based on the density-functional theory (DFT) and the quasi-harmonic Debye model. We used the local spin density approximation (LSDA) and LSDA+U approaches for the exchange-correlation potential. The equilibrium lattice parameter, bulk modulus, transition pressure, elastic constants and their related parameters such as Poisson's ratio, Young modulus, shear modulus and Debye temperature were calculated. The good agreement of our calculations with experiment and theory for the other works suggests that our assignment is very correct. According to the critical value of B/G ratio, the compounds have a ductile behavior. The strong single-site Coulomb repulsion problem in the localized 5f-electrons of Np actinide element was treated with LSDA+U to describe perfectly the electronic properties. The temperature and pressure dependence of cell volume, bulk modulus, heat capacity and Debye temperature are examined through the quasi-harmonic Debye model, systematically in various pressures and at temperature ranging from 0 K to 500 K.