First-principles study on the structural, electronic, elastic and thermal properties of Ag₂O₂S

Using first-principles density functional theory and machine learning method, we predict a new structure of Ag₂O₂S with space group P-3m1. Through the plane wave pseudopotential approach, the electronic structure, elastic constant, bulk modulus, shear modulus, Young's modulus, lattice thermal conductivity and phonon relaxation time for Ag₂O₂S are systematically studied. The results show that the structure is dynamically and mechanically stable, and has a high anisotropic nature. Because of softening phonon and elastic instability, Ag₂O₂S occurs a phase transition at about 22.8–23.8 GPa. Moreover, the significant acoustic optical coupling in Ag₂O₂S is observed in the phonon spectra. The predicted lattice thermal conductivity is 3.85 W m−1 K−1 at 300 K, which would have a promising application in the thermal insulation field. The phonon relaxation times in the normal process are smaller that of the umklapp process above 300 K, leading to the decrease of lattice thermal conductivity at high temperature. (author)