Thermoelectric and vibrational properties of Be₂C, BeMgC and Mg₂C using first-principles method

Transport coefficients are calculated combining first-principles calculations with the Boltzmann transport theory. Electronic states obtained in terms of the k-space eigen-energies from the crystalline orbital program, based on density functional theory, are Fourier transformed and interfaced with the transport equations modeled in the BoltzTraP. The calculations are performed for Be₂C, Mg₂C, and the BeMgC mixed crystal. The Seebeck coefficient, electronic thermal conductivity and the power factor are calculated. Further, the transport coefficients are linked to find the electronic fitness function to compare the performance with other thermoelectric materials. The procedure can also be applied to study the thermoelectric properties of other materials. The vibrational frequencies at the Brillouin zone centre are calculated generating a Hessian matrix from the analytical gradients of the energy with respect to atomic coordinates in the three antifluorite crystals. Moreover, the static, high frequency dielectric constants and Born effective charges are calculated to find splitting in the longitudinal optic and transverse optic modes. Results are compared with the data wherever available in the literature and a very good agreement is found in most cases.