First-principles prediction of the structural, elastic, thermodynamic, electronic and optical properties of Li4Sr3Ge2N6 quaternary nitride

• Some physical properties of the quaternary nitride Li4Sr3Ge2N6 have been predicted.
• Elastic parameters reveal that Li4Sr3Ge2N6 is mechanically stable but anisotropi.
• Li4Sr3Ge2N6 is an indirect semiconductor.
• The fundamental indirect band gap changes to direct one under pressure effect.
• The optical properties exhibit noticeable anisotropy.

Structural parameters, elastic constants, thermodynamic properties, electronic structure and optical properties of the monoclinic Li4Sr3Ge2N6 quaternary nitride are investigated theoretically for the first time using the pseudopotential plane-wave based first-principles calculations. The calculated structural parameters are in excellent agreement with the experimental data. This serves as a proof of reliability of the used theoretical method and gives confidence in the predicted results on aforementioned properties of Li4Sr3Ge2N6. The predicted elastic constants Cij reveal that Li4Sr3Ge2N6 is mechanically stable but anisotropic. The elastic anisotropy is further illustrated by the direction-dependent of the linear compressibility and Young’s modulus. Macroscopic elastic parameters, including the bulk and shear moduli, the Young’s modulus, the Poisson ratio, the velocities of elastic waves and the Debye temperature are numerically estimated. The pressure and temperature dependence of the unit cell volume, isothermal bulk modulus, volume expansion coefficient, specific heat and Debye temperature are investigated through the quasiharmonic Debye model. The band structure and the density of states of