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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >High-pressure study of lithium azide from density-functional calculations
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High-pressure study of lithium azide from density-functional calculations

机译：密度函数计算法对叠氮化锂的高压研究

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The structural, electronic, optical, and vibrational properties of LiN _3 under high pressure have been studied using plane wave pseudopotentials within the generalized gradient approximation for the exchange and correlation functional. The calculated lattice parameters agree quite well with experiments. The calculated bulk modulus value is found to be 23.23 GPa, which is in good agreement with the experimental value of 20.5 GPa. Our calculations reproduce well the trends in high-pressure behavior of the structural parameters. The present results show that the compressibility of LiN_3 crystal is anisotropic and the crystallographic b-axis is more compressible when compared to a- and c-axes, which is also consistent with experiment. Elastic constants are predicted, which still awaits experimental confirmation. The computed elastic constants clearly show that LiN_3 is a mechanically stable system and the calculated elastic constants follow the order C_(33) > C_(11) > C_(22), implying that the LiN_3 lattice is stiffer along the c-axis and relatively weaker along the b-axis. Under the application of pressure the magnitude of the electronic band gap value decreases, indicating that the system has the tendency to become semiconductor at high pressures. The optical properties such as refractive index, absorption spectra, and photoconductivity along the three crystallographic directions have been calculated at ambient as well as at high pressures. The calculated refractive index shows that the system is optically anisotropic and the anisotropy increases with an increase in pressure. The observed peaks in the absorption and photoconductivity spectra are found to shift toward the higher energy region as pressure increases, which implies that in LiN_3 decomposition is favored under pressure with the action of light. The vibrational frequencies for the internal and lattice modes of LiN3 at ambient conditions as well as at high pressures are calculated from which we predict that the response of the lattice modes toward pressure is relatively high when compared to the internal modes of the azide ion.
机译：LiN _3在高压下的结构，电子，光学和振动性质已经在交换和相关函数的广义梯度近似内使用平面波假电位进行了研究。计算出的晶格参数与实验非常吻合。发现计算的体积模量值为23.23 GPa，与20.5 GPa的实验值非常吻合。我们的计算很好地再现了结构参数的高压行为趋势。目前的结果表明，与a轴和c轴相比，LiN_3晶体的可压缩性是各向异性的，并且晶体学b轴的可压缩性更高。可以预测弹性常数，尚待实验确认。计算出的弹性常数清楚地表明LiN_3是一个机械稳定的系统，并且计算出的弹性常数遵循C_（33）> C_（11）> C_（22）的顺序，这意味着LiN_3晶格在c轴上相对较硬，相对沿b轴变弱。在施加压力下，电子带隙值的幅度减小，表明该系统具有在高压下变成半导体的趋势。沿三个晶体学方向的光学特性（如折射率，吸收光谱和光电导率）已在环境和高压下进行了计算。计算出的折射率表明该系统是光学各向异性的，并且各向异性随着压力的增加而增加。发现在吸收光谱和光电导光谱中观察到的峰值随着压力的增加而向更高的能量区域移动，这表明在LiN_3中，在光的作用下，在压力下有利于分解。计算了LiN3的内部和晶格模式在环境条件以及高压下的振动频率，从中我们可以预测，与叠氮化物离子的内部模式相比，晶格模式对压力的响应相对较高。

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