We present first-principles calculations on the structural, mechanical, electronic, thermodynamic, lattice dynamic and magnetic properties of RbN in the CsCl, rocksalt (Rs) and zinc-blende (ZB) structures centred on spin-polarised density functional theory (DFT). It was established that in all the three structures, ferromagnetic (FM) state is more stable than the non-magnetic (NM) state. The results show that RbN exhibits half-metallic characteristics at the equilibrium lattice parameters and have small energy gaps of 1.205, 1.092 and 1.364 eV for CsCl, Rs and ZB structures respectively. We find that only the CsCl and Rs structures are mechanically, lattice dynamically and thermodynamically stable. Furthermore, the structures exhibit equal integer magnetic moment of $2 \mu_\rm{B}$ approximately.

In this paper, novel perovskite compounds XMgO$_3$ (X = Na, K and Rb) have been investigated intensively in the framework of density functional theory. The results of the magnetic and electronic properties of the perovskite reveal that the three perovskites are ferromagnets and are half-metals which make them idealfor spintronic devices. The magnetic moment of each perovskite is 3 μB. The compounds are also found to be mechanically and thermodynamically stable. From their B/G ratios, it is found that they are ductile and have highspecific heat capacities. When subjected to strains below their equilibrium lattice constants, the three compounds lose their magnetic moment.