Abstract:
We present a detailed comparative study of the electronic and mechanical properties of the early actinide
mononitrides and dinitrides within the framework of the Perdew–Burke–Ernzerhof generalized gradient
approximation (GGA [PBE]) and GGA + U implementations of density functional theory with the inclusion
of spin–orbit coupling. The dependence of selected observables of these materials on the effective U parameter
is investigated in detail. The properties include the lattice constant, bulk modulus, charge density
distribution, hybridization of the atomic orbitals, energy of formation and the lattice dynamics. The
inclusion of the Hubbard U parameter results in a proper description of the 5f electrons, and is subsequently
used in the determination of the structural and electronic properties of these compounds. The
mononitrides and dinitrides of the early actinides are metallic except for UN2, which is a semiconductor.
These actinide nitrides are non-magnetic with the exception of UN, NpN, PuN, NpN2 and PuN2 that are
magnetic systems with orbital-dependent magnetic moments oriented in the z-axis. We observed that
ThN2 is elastically unstable to isotropic pressure. We discovered that UN2 is thermodynamically unstable,
but may be stabilized by N vacancy formation.
