Structural, elastic, electronic, optical and thermal properties of c-SiGe2N4

摘要

We have investigated the structural, elastic, electronic, optical and thermal properties ofc-SiGe2N4 by using the ultrasoft pseudopotential density functional method within the generalized gra-dient approximation. The calculated structural parameters, including the lattice constant, the internalfree parameter, the bulk modulus and its pressure derivative are in agreement with the available data.The independent elastic constants and their pressure dependence, calculated using the static finite straintechnique, satisfy the requirement of mechanical stability, indicating that c-SiGe2N4 compound could bestable. We derive the shear modulus, Young's modulus, Poisson's ratio and Lame's 'coefficients for idealpolycrystalline c-SiGe2N4 aggregate in the framework of the Voigt-Reuss-Hill approximation. We estimatethe Debye temperature of this compound from the average sound velocity. Band structure, density of states,Mulliken charge populations and pressure coefficients of energy band gaps are investigated. Furthermore, inorder to understand the optical properties of c-SiGe2N4, the dielectric function, refractive index, extinctioncoefficient, optical reflectivity and electron energy loss are calculated for radiation up to 40 eV. Thermaleffects on some macroscopic properties of c-SiGe2N4 are predicted using the quasi-harmonic Debye modelin which the lattice vibrations are taken into account. We have obtained successfully the variations of theprimitive cell volume, volume expansion coefficient, heat capacities and Debye temperature with pressureand temperature in the ranges of 0-40 GPa and 0-2000 K. For the first time, the numerical estimates ofthe elastic constants and related parameters, and the thermal properties are performed for c-SiGe2N4.