Magnetic, electronic and optical properties of lanthanide hydrides, GdH2 and GdH3

• The magnetic phase is much more stable than the nonmagnetic phase for GdH2 or GdH3 both at zero and high pressure.
• The calculations clearly show that the AFM fcc GdH2 and hcp GdH3 attribute to metal and semiconductor respectively.
• The AFM fcc GdH2 and hcp GdH3 have similar magnetic moment and ionic–covalent bonding character.
• The semiconducting GdH3 may have a 1.55 eV fundamental band gap.
• The complex dielectric function and refractive index are predicted for the hcp GdH3 in the whole energy range.

The structural, magnetic, electronic and optical properties as well as phase stabilities under pressure for GdH2 and GdH3 are investigated using density function theory. The non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) phases are considered for the total energy calculations. The magnetic phase is much more stable than the nonmagnetic phase both at ambient pressure and high pressure for the cubic GdH2 or hexagonal GdH3, but the antiferromagnetic phase is only slightly more stable than the ferromagnetic phase at ambient pressure in the two cases. With increasing pressure, the antiferromagnetic fcc GdH2 may transform to the ferromagnetic phase, while the antiferromagnetic hcp GdH3 keeps stable in the interesting pressure range. The pure theoretical calculations further indicate that there is a structural transition from hcp to fcc for GdH3 at about 9.8 GPa. In addition, the calculations of band structures and densities of states clearly show that the antiferromagnetic fcc GdH2 attributes to metal, whereas the antiferromagnetic hcp GdH3 attributes to semiconductor, but both have similar ionic–covalent bonding character. The semiconducting GdH3 may have a 1.55 eV fundamental band gap. Under the fundamental band gap, the complex dielectric function and refractive index are predicted for the hcp GdH3 in the whole energy range.