本文選題：第一性原理分子動力學　切入點：非金屬-金屬轉(zhuǎn)變　出處：《西南大學》2017年碩士論文　論文類型：學位論文

【摘要】：含氫量高的富氫化合物是較好的儲能材料,而甲烷是富氫體系中最簡單的飽和碳氫化合物。甲烷也是地幔、天王星和海王星等巨行星的主要成分,在這些行星內(nèi)部溫度處于2000 K-8000 K,壓強處于20 GPa-600 GPa。研究甲烷在高溫高壓下電子結(jié)構(gòu)、相態(tài)(包括固相、液相、氣相和等離子相等)的變化、甲烷分子的解離和原子重組,及其對物理性質(zhì)(包括熱、電、光性質(zhì)等)的影響,對于人們認識極端條件下凝聚態(tài)物質(zhì)具有重要的科學意義;也利于近代自然科學和工程技術(shù)中的幾個重大問題,例如:能源問題、天體演化問題、金屬氫等問題的解決。本文將采用基于密度泛函理論的第一性原理模擬,研究高溫高壓下甲烷的物態(tài)方程、離解相變和導電性,具體內(nèi)容包括以下幾個方面:1.我們采用基于密度泛函理論的分子動力學模擬計算了密度為0.60g/cm3-2.5g/cm3、溫度為1000K-8000K,對應的壓強為3.6GPa-332GPa范圍內(nèi)流體甲烷的物態(tài)方程,并作出不同密度下的等容線,我們觀察到除0.60 g/cm3以外的各個密度下都存在壓強滯漲或降低的區(qū)域,即((?)P/(?)T)≤0。通過對計算得到的數(shù)據(jù)進行擬合,得到十分吻合的擬合公式。2.通過構(gòu)型抽取和徑向分布函數(shù)分析甲烷在高溫高壓下化學組分變化情況和原子鍵合情況,發(fā)現(xiàn)在極端條件下甲烷發(fā)生化學分解,形成飽和烷烴如乙烷、丁烷等,還有不飽和烷烴如烯烴、炔烴等,最終會聚合成長烴鏈和一些氫氣或者自由的氫原子,但是在甲烷的分解過程中我們并沒有發(fā)現(xiàn)金剛石結(jié)構(gòu)碳形成。除此之外發(fā)現(xiàn)等容線上壓強滯漲或降低的區(qū)域與甲烷的化學分解過程緊密相關(guān)。3.通過計算電子能帶和直流電導率隨溫度和壓強的變化規(guī)律,發(fā)現(xiàn)甲烷在高溫高壓下發(fā)生非金屬-金屬轉(zhuǎn)變,并給出了體系發(fā)生非金屬-金屬轉(zhuǎn)變的臨界溫度為5000 K,此時的壓強為8 GPa。通過對電子分波態(tài)密度分析,發(fā)現(xiàn)體系具有很高的直流電導率主要是自由的氫原子和碳鏈上碳原子的貢獻。最后我們給出了甲烷流體非金屬-金屬的相變曲線。本文采用基于密度泛函理論的分子動力學模擬計算溫稠密甲烷熱力性質(zhì)的影響,研究在高溫高壓下甲烷流體的物態(tài)方程、化學分解和非金屬-金屬轉(zhuǎn)變。
[Abstract]:Hydrogen rich compounds with high hydrogen content are better materials for energy storage, while methane is the simplest saturated hydrocarbon in hydrogen rich systems. Methane is also a major component of giant planets such as the mantle, Uranus and Neptune. The internal temperature of these planets is 2 000 K and the pressure is 20 GPa-600 GPA. The changes of electronic structure, phase states (including solid, liquid, gas and plasma), dissociation and atomic recombination of methane at high temperature and high pressure are studied. And its effects on physical properties (including thermal, electrical, optical properties, etc.) are of great scientific significance to people's understanding of condensed matter under extreme conditions, and are conducive to several important problems in modern natural science and engineering technology, For example, the energy problem, the evolution of celestial bodies, the solution of metal hydrogen, etc. In this paper, the first principle simulation based on density functional theory is used to study the equation of state, dissociation phase transition and electrical conductivity of methane at high temperature and high pressure. The specific contents include the following aspects: 1.We use the molecular dynamics simulation based on density functional theory to calculate the equation of state of the fluid methane in the range of 3.6GPa-332GPa with density of 0.60g / cm3-2.5gcm3, temperature of 1000K-8000K, and the isovolumetric lines at different densities. We have observed that there are areas where the pressure stagflation or decrease exists at all densities except 0.60 g / cm3. P / P? T) 鈮，

本文編號：1561055