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arXiv 1311.0979cond-mat.mtrl-sci
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KN $_3$和RbN $_3$的结构、弹性和动力学性质:范德华密度泛函研究

Structure, elastic and dynamical properties of KN$_3$ and RbN$_3$: A van der Waals density functional study

K. Ramesh Babu, G. Vaitheeswaran

摘要:

本文采用第一性原理研究了层状含能碱金属叠氮化物KN $_3$和RbN $_3$的结构、弹性、振动和热力学性质。所有计算均采用平面波赝势方法进行,考虑和不考虑范德华相互作用。通过引入色散修正,计算得到的基态结构性质得到了较大程度的改善,表明范德华相互作用对这些体系的物理性质起着重要作用.用这两种方法计算了四元体系KN $_3$和RbN $_3$的弹性常数和相关的体相力学性能,发现它们是机械稳定的体系。计算的弹性常数的大小以RbN $_3$ $<$ KN $_3$的顺序增加,这意味着KN $_3$具有更高的弹性刚度,这一事实也被KN $_3$的体积模量、剪切模量和杨氏模量的值比RbN $_3$更高所证实。此外,计算出的弹性常数遵循不等式C $_{33}$ $<$ C $_{11}$,这表明叠氮化物晶格的沿a轴的分子间相互作用的数目多于沿c轴的。已经提出了一个相关的金属叠氮化物的分解现象与计算的弹性常数。实验报告的振动频率在伽马点的准确再现本计算。此外,我们还提供了热力学性质,如热容,与实验进行了比较。

英文摘要:

We report a detailed first principles study on the structural, elastic, vibrational and thermodynamic properties of layered structure energetic alkali metal azides KN$_3$ and RbN$_3$. All the calculations were carried out by means of plane wave pseudopotential method with and without including van der Waals interactions. The calculated ground state structural properties are improved to a greater extent by the inclusion of dispersion corrections, implies that the van der Waals interactions play a major role on the physical properties of these systems. The elastic constants and the related bulk mechanical properties for the tetragonal KN$_3$ and RbN$_3$ have been calculated using both the methods and found that the compounds are mechanically stable systems. The magnitude of the calculated elastic constants increases in the order RbN$_3$ $<$ KN$_3$ implying higher elastic stiffness for KN$_3$, the fact also confirmed by the higher values of bulk, shear and Young's moduli of KN$_3$ than RbN$_3$. Moreover, the calculated elastic constants follows the inequality C$_{33}$ $<$ C$_{11}$ which indicates the presence of more number of intermolecular interactions along a-axis over c-axis of the azide lattices. A correlation has been proposed to relate the calculated elastic constants to the decomposition phenomena for the metal azides. The experimentally reported vibrational frequencies at the gamma point were exactly reproduced by the present calculations. In addition, we also present the thermodynamic properties such as heat capacity which compares well with the experiment.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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