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首页> 外文期刊>Physical review >First-principles study of phonons and related ground-state properties and spectra in Zn-IV-N_2 compounds
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First-principles study of phonons and related ground-state properties and spectra in Zn-IV-N_2 compounds

机译：Zn-IV-N_2化合物中声子及其相关基态特性和光谱的第一性原理研究

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The Zn-IV-N_2 compounds, with the group-IV element Si, Ge, and Sn, which have a common crystal structure closely related to the wurtzite-structure form a series analogous to the group-III nitrides GaN, A1N, and InN, respectively. Calculations of the phonons and related quantities in these materials are reported here using the density-functional perturbation-theory linear-response approach in the local-density approximation and using a plane-wave pseudopotential method. We focus on spectra, such as the imaginary part of the dielectric function and the energy-loss function as measurable by infrared absorption or reflectivity, and the Raman spectra. We also present phonon densities of states, band dispersions, and related integrated thermo-dynamic quantities such as the specific heat, and Helmholtz free energy and entropy as functions of temperature. Structural and elastic properties such as the lattice constants and bulk moduli are also reported. Finally, high-frequency and static dielectric tensors are presented. The trends in the series and the relation to the corresponding III-N nitrides are discussed. It is found that the bimodal bond-length distribution with IV-N bonds shorter than the Zn-N bonds (even for Sn) strongly modifies the spectra from those in III-N nitrides. While in ZnGeN_2 and ZnSnN_2 folded acoustic-like modes are clearly separated from the optic type modes, this is not the case in ZnSiN_2. The calculated Bom effective charges indicate that ZnGeN_2 has the lowest ionicity of the three materials.
机译：具有与纤锌矿结构密切相关的共同晶体结构的，具有IV族元素Si，Ge和Sn的Zn-IV-N_2化合物形成类似于III族氮化物GaN，AlN和InN的系列， 分别。这些材料中声子和相关量的计算方法是在局部密度近似中使用密度泛函微扰理论线性响应方法，并使用平面波pseudo势方法进行计算。我们专注于光谱，例如介电函数的虚部和能量损失函数（可通过红外吸收或反射率测量）和拉曼光谱。我们还给出了状态的声子密度，能带色散以及相关的综合热力学量，例如比热，亥姆霍兹自由能和熵随温度的变化。还报道了结构和弹性性质，例如晶格常数和体积模量。最后，给出了高频和静态介电张量。讨论了该系列的趋势及其与相应的III-N氮化物的关系。已经发现，IV-N键比Zn-N键短的双峰键长分布（即使对于Sn也是如此）强烈地改变了III-N氮化物中的光谱。尽管在ZnGeN_2和ZnSnN_2中，折叠声状模与光学型模明显分开，但在ZnSiN_2中却不是这样。计算出的Bom有效电荷表明ZnGeN_2具有三种材料中最低的离子性。

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