高温高压下碳化钨晶体的结构、力学、电子、光学以及热力学性能的第一性原理计算

本文利用密度泛函理论中的广义梯度近似对碳化钨晶体的三种结构(碳化钨相、闪锌矿相以及纤锌矿相)进行了优化,得到能量最低的稳定构型,并在此基础上计算了它的力学、电子、光学和高温高压下的热力学性质.研究表明:在0～300 GPa压力范围内,碳化钨相具有最高的稳定性.同时,高压下碳化钨相的弹性常数满足Born-Huang准则,且0 GPa和300 GPa下的声子色散没有虚频,证明了高压下碳化钨相的静力学稳定性和动力学稳定性.电子性质表明了碳化钨的金属性.光学性质表明碳化钨在高能区很难吸收光.热力学性质的研究表明:体积比V/V_0对压强的变化更敏感;高温时C_V曲线近似一条直线;给定压强下热膨胀系数α在600 K温度以上增长非常缓慢;压强对德拜温度Θ_D的影响较大;在低压下格林艾森系数γ的变化较大.

First-principles study of structural, elastic, electronic, optical and thermodynamic properties of tungsten carbide at high temperature and high pressure

In the framework of the density functional theory, the generalized gradient approximation is used to optimize the geometrical structure of tungsten carbide, and the lowest-energy structure was obtained. Then mechanical properties, electronic properties, optical properties and the thermodynamic properties under different pressures and different temperatures were calculated. The results showed that among the tungsten carbide phase, the sphalerite phase, and the wurtzite phase, the tungsten carbide phase has the highest stability. The properties of the tungsten carbide phase were calculated: its elastic constants satisfy the Born-Huang criterion and it has mechanical stability under both normal pressure and high pressure. The calculation results showed that tungsten carbide has a large bulk modulus and shear modulus, suggesting that it has a large hardness. Energy band structure and electronic density of states confirm the metallicity of tungsten carbide. The phonon dispersions at 0 GPa and 300 GPa were calculated to verify the dynamic stability. The thermodynamic properties of tungsten carbide under high temperature and high pressure were studied, including thermodynamic expansivity, heat capacity, Debye temperature and Grüneisen parameter. And the heat capacity is close to the Dulong-Petit limit at high temperatures, the Debye temperature is less affected by the temperature than the pressure. In the study of optical properties, according to absorption coefficient spectrum, it is found that tungsten carbide is difficult to absorb light in the high energy region, and this conclusion is confirmed by the combination of refractive index, extinction coefficient, loss function and conductivity. In conclusion, the relevant properties of tungsten carbide are studied in this paper, our calculation results are of significance for determining the special properties of tungsten carbide under high temperature and high pressure, and provide a relatively reliable theoretical basis for future research.