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arXiv 1804.09072cond-mat.mtrl-scicond-mat.dis-nn
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\textit{ab initio}分子动力学模拟与进化搜索相结合的无定形氮聚合物结构演化

Structural evolution of amorphous polymeric nitrogen from \textit{ab initio} molecular dynamics simulations and evolutionary search

Dominika Melicherová, Oto Kohulák, Dušan Plašienka, Roman Martoňák

摘要:

具有单键的聚合氮可以在高压下从分子形式产生,并且由于三键和单键之间的大能量差,它作为高能材料是令人感兴趣的。然而,它的结构和性质仍然没有得到很好的理解。我们研究了无定形氮的\textit{ab initio}模拟,采用分子动力学和进化算法。在120 GPa压力下,通过热液淬冷、压力诱导分子晶体非晶化和进化搜索等方法制备了非晶氮。发现所有三种无定形形式在结构上相似。我们详细研究了该系统在100 K下从120 GPa减压到零压时的结构演化。当压力大于100 GPa时,体系主要由三配位原子(80%)通过单键连接而成,同时也存在一些由二配位原子组成的短链。减压时,3配位原子的数量迅速减少到60 GPa以下,并产生更长的链。在20 GPa下,系统开始也产生N个$_2$分子,并且在$p=0$的最终结构包含在聚合物网络内的分子,所述聚合物网络主要由2配位原子构成的较长链组成。除了结构,我们还研究了系统的振动和电子性质,并估计了在环境压力下可以存储在非晶氮中的能量。

英文摘要:

Polymeric nitrogen with single bonds can be created from the molecular form at high pressure and due to large energy difference between triple and single bonds it is interesting as energetic material. Its structure and properties are, however, still not well understood. We studied amorphous nitrogen by \textit{ab initio} simulations, employing molecular dynamics and evolutionary algorithms. Amorphous nitrogen was prepared at pressure of 120 GPa by quenching from hot liquid, by pressure-induced amorphization of molecular crystal and by evolutionary search. All three amorphous forms were found to be structurally similar. We studied in detail the structural evolution of the system upon decompression from 120 GPa to zero pressure at 100 K. At pressures above 100 GPa, system consists mainly of 3-coordinated atoms (80 \%) connected by single bonds while some short chains made of 2-coordinated atoms are also present. Upon decompression, the number of 3-coordinated atoms rapidly decreases below 60 GPa and longer chains are created. At 20 GPa the system starts to create also N$_2$ molecules and the ultimate structure at $p=0$ contains molecules inside a polymeric network consisting dominantly of longer chains made of 2-coordinated atoms. Besides structure, we also study vibrational and electronic properties of the system and estimate the amount of energy that could be stored in amorphous nitrogen at ambient pressure.

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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