The structural, elastic, anisotropic, and thermodynamic properties of P3m1-BC₇ and Pmm2-BC₇ have been studied in this paper utilizing first-principles calculations. In comparison with the elastic properties of Pmm2-BC₇, P3m1-BC₇ exhibits slightly higher values in bulk modulus and B/G, with similar values in shear modulus, the Young modulus, and the Poisson ratio. The calculated Pugh modulus ratio (B/G) and the Poisson ratio demonstrates P3m1-BC₇ from brittle to ductile at 93.60 and 93.73 GPa, respectively. Calculations of shear anisotropic factor, universal elastic anisotropy index, shear modulus, the Young modulus, and the Poisson ratio for BC₇ then demonstrate that Pmm2-BC₇ exhibits a larger elastic anisotropy than P3m1-BC₇. Quasi-harmonic Debye model is finally applied to investigate the Debye temperature, the coefficient of thermal expansion, heat capacity and Grüneisen parameter of Pmm2-BC₇ and P3m1-BC₇.
Based on the density functional theory and the quasi-harmonic Debye model, the structural and thermodynamic properties of I-4m2-BCN have been studied in this paper. Some structural parameters are presented in this work. All of these results are in excellent agreement with the other available results. The anisotropy of elastic properties are also studied systematically in this paper. Finally, the thermodynamic properties of I-4m2-BCN are also researched through the quasi-harmonic Debye model. The relations among the thermal expansion α, the Debye temperature Θ_{D}, the heat capacity C_V and C_P, the Grüneisen parameter γ , entropy S, and the Gibbs free energy G with pressure P and temperature T are studied systematically.
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