First-principles calculation of the electronic structure, chemical bonding, and thermodynamic properties of β-US2**Project supported by the National Natural Science Foundation of China (Grant Nos. 21371160 and 21401173).

Abstract

The electronic structure, magnetic states, chemical bonding, and thermodynamic properties of β-US2 are investigated by using first-principles calculation through the density functional theory (DFT) +U approach. The obtained band structure exhibits a direct band gap semiconductor at Γ point with a band gap of 0.9 eV for β-US2, which is in good agreement with the recent experimental data. The charge-density differences, the Bader charge analysis, and the Born effective charges suggest that the U–S bonds of the β-US2 have a mixture of covalent and ionic characters, but the ionic character is stronger than covalent character. The Raman-active, infrared-active, and silent modes at the Γ point are further assigned and discussed. The obtained optical-mode frequencies indicate that the three apparent LO–TO (longitudinal optical–transverse optical) splittings occur in B1u, B2u, and B3u modes, respectively. Furthermore, the Helmholtz free energy ΔF, the specific heat ΔE, vibrational entropy S, and constant volume CV are studied over a range from 0 K∼100 K. We expect that our work can provide some valuable information for further experimental investigation of the dielectric properties and the infrared reflectivity spectrum of uranium chalcogenide.