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標題: | 高壓下氮氧化物結構搜尋 High Pressure Phases of N-rich NxO Compounds by Random Structure Search |
作者: | Hao-Chien Hung 洪豪謙 |
指導教授: | 王玉麟 |
關鍵字: | 密度泛函理論,隨機結構搜尋,氮氧化物,高壓結構,形成焓, Density functional theory,Random structure search,nitrogen oxide systems,high pressure structures,formation enthalpy, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 本篇論文運用密度泛函理論(Density functional theory)的模擬運算,及隨機結構搜尋(Random structure search)的方式計算高壓下的氮氧系統(N2/O2 binary system)結構。根據我們模擬結果,高壓下系統總能量較低的氮氧系統可細分成五種結構,包含分子(molecular)、聚合(polymeric)、薄片形(sheet-like)、厚板形(slab-like)及延伸網狀結構(extended network structures)。隨著氮氧比例增加,且系統壓力達到數十個GPa,我們的計算結果顯示氮氧系統會傾向於後者。這現象背後的機制是在於能夠形成三配位數的氮原子能在高壓下有較低的系統能量,因為較高的配位數能組成較密集的系統,相較於單或雙配位數的氮原子來說三配位數氮原子能使系統擁有較低的體積。另外有趣的一點是,在N4O 系統,我們發現一個從未被提及的分子結構,我們稱之為雙五角結構(Double pentagon, N8O2),且這個結構在壓力介於61到85 GPa之間能夠擁有相較較低的系統總能量,壓力高於85 GPa後才會轉變成延伸網狀結構。關於形成焓(formation enthalpies)以及各結構的細節也將會在此篇論文中被提及。 We perform the random structure search for N2/O2 binary system under high pressure within the framework of density functional theory. We have found five types of structures to be energetically competitive under different circumstances. Including molecular, polymeric, sheet-like, slab-like and extended network structures. As N/O ratio increases up to 4 and pressure increases up to tens of GPa, our results show the tendency that the binary system prefers the last. The mechanism behind this phenomenon is that the systems in which all the nitrogen atoms are in three-fold coordination become energetically favorable under high pressure, since them can form extended network structures that have smaller volume. Intriguingly, for N4O system we found one novel molecular structure, named double pentagon (N8O2), which to our knowledge has not been reported before can be relatively stable within the pressure ranged from 61 to 85 GPa. Above 85 GPa the extended network structure becomes energetically favorable. The formation enthalpies and the details of each structure are presented and discussed. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/69721 |
DOI: | 10.6342/NTU201800840 |
全文授權: | 有償授權 |
顯示於系所單位: | 物理學系 |
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