GGA+U study on phase transition, optoelectronic and magnetic properties of AmO2 with spin–orbit coupling

• AmO2 is antiferromagnetic and stable in the Fm3m phase under ambient conditions.
• It makes structural transition from the Fm3m to the Pnma phase at 55.91 GPa.
• Columbic repulsion parameter U correctly predicted the electronic state of AmO2.
• This compound absorbs strongly in the UV region.

In this work, we have investigated the structural, phase transition, optoelectronic and magnetic properties of AmO2 using the full potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The exchange-correlation potential was treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approximation (where U denotes the Hubbard Coulomb energy U term) is employed to treat the f electrons properly. The structurally stable AmO2 compound is the Fm3m phase and at a pressure between 40 and 60 GPa underwent a phase transition to the Pnma phase. Our present calculations have considered ferromagnetic and simple antiferromagnetic ground states and the AF state is favored. However, the experimental situation suggests a complex magnetic structure, perhaps involving multipolar ordering. Our band structure calculation with GGA and GGA+U predicted the metallic behavior of AmO2; however, with the spin–orbit coupling (SOC) added to the Coulomb energy U term, semiconducting ground states with antiferromagnetism is correctly predicted. The projected density of states from the energy-band structure indicates that the band gap opening is governed by the partially filled Am “5f” state, and the calculated gap is approximately 1.29 eV. Moreover, the optical properties reveal strong response of AmO2 in the UV region.