Structural, magnetic, and dynamic properties of PuH2+x (x= 0, 0.25, 0.5, 0.75, 1): A hybrid density functional study

Plutonium (Pu) can react with hydrogen to form complicated continuous solid solutions with unusual chemical and physical properties. The PBE0 hybrid density functional under the framework of full-potential linearized augmented plane wave plus local orbitals is employed to investigate the structural, magnetic, lattice vibrations, and thermodynamic properties of face-centered cubic plutonium hydride (PuH2+x, x = 0, 0.25, 0.5, 0.75, 1). The decreasing trend with increasing x of the optimized lattice parameters is in reasonable agreement with experimental findings. According to the calculated formation enthalpies of PuH2+x compounds, all PuHx for both ferromagnetic(FM) and antiferromagnetic (AFM) phase are thermodynamically favorable, and the FM phase plutonium hydride is more favorable than the AFM phases. The characteristic Raman-active and the infrared-active modes at the center (Γ point) of the first Brillouin zone were further assigned and discussed. Finally, the free energy F, internal energy E, vibration enthalpy S, and constant-volume specific heat CV of PuH2+x are calculated in the range of 0-1000 K.