本論文利用basin-hopping (BH)方法搭配tight-binding(TB)勢能預測出極細鎢奈米線(W nanowire)與鎢奈米管(W nanotube)之穩定結構，再利用分子動力學(Molecular dynamic)與密度泛函理論-分子動力學(Density functional theory-Molecular dynamic, DFT-MD)探討鎢奈米線與奈米管之機械性質與熱穩定性，最後以密度泛函理論(Density functional theory, DFT)分析螺旋鎢奈米管之氧化行為與路徑。由分析奈米線與奈米管的機械性質結果可得，鎢奈米線及奈米管具有很好的延性，並且楊氏模數隨尺寸縮小而下降。在熱穩定性方面，奈米線在溫度1300K以下結構都能夠穩定，而鎢奈米管熔點則低於鎢奈米線約在860K達到熔點。在電子性質方面，藉由分析不同尺寸下的鎢奈米線與奈米管的局部電子態密度，可以了解鎢奈米線與奈米管的電子軌道雜化的情形，結果顯示鎢的一維奈米結構比鎢塊材有更好的電子遷移能力，而在6種不同的鎢奈米線/管結構中又以螺旋鎢奈米管的化學活性最佳，因此我們選擇螺旋鎢奈米管以Eley-Radeal(ER)機制計算CO分子在表面的氧化路徑並與W(111)表面做比較，接著計算CO氧化過程中的局部電子態密度(Partial density of states, PDOS)來了解鎢奈米管與吸附分子間的相互作用，由計算結果可得在鎢奈米管上有比較小的能障0.468 eV，相較於W(111)表面更容易催化CO分子，這表示鎢奈米管具有更優越的催化活性能夠取代其他結構做為催化劑的材料。

In this study, the structures of ultrathin W nanowires and nanotubes were predicted by the simulated annealing basin-hopping method (SABH) with the tight-binding potential. The mechanical properities and thermal stability of the W nanowires and nanotubes were further examined by the molecular dynamic (MD) calculation and density functional theory molecular dynamics (DFT-MD) simulation. Furthermore, the oxidation of CO molecules on W helical nanotube has also been investigated by DFT calculations. The mechanical properties results of nanowires and nanotubes are presented that W nanowires and nanotubes possess good ductility and their Young's moduli decrease with decreasing of size. In terms of thermal stability, these W nanowires are still stable at temperatures as high as 1300 K. In the electronic properties, we analyze the PDOS of W nanowires and nanotubes with different sizes to understand orbital hybridization. The results show that one-dimension W nanostructures possess better charge transfer capabilities than bulk W, and the W helical nanotube has the best chemical activity in six structures. Therefore, Eley-Radeal (ER) mechanism is considered for examining and comparing the mechanism of CO oxidation on W helical nanotube and W (111) surface. Then the PDOS of the CO oxidation were analyzed to understand the interaction between W nanotube and adsorbed molecules. The calculations show that the energy barrier for W nanotubes is only 0.468 eV, lower than W(111) surface, this result means that W nanotubes have good catalytic activity which can be replaced other structures as catalysts.

論文審定書 I
致謝 II
中文摘要 III
英文摘要 IV
目錄 VI
圖次 VIII
表次 X
第一章 緒論 1
1.1 研究目的與動機 1
1.2 鎢奈米線與奈米管文獻回顧 3
1.3 本文架構 6
第二章 模擬方法與理論介紹 7
2.1 分子靜力學理論 7
2.1.1 Basin-hopping計算法 7
2.1.2 懲罰函數(Penalty function) 8
2.1.3 勢能函數 (Potential function) 9
2.2 密度泛函理論(DENSITY FUNCTIONAL THEORY, DFT) 11
2.2.1 電子密度 11
2.2.2 Hohenberg-Kohn model(HK model) 12
2.2.3 Kohn-Sham equation (KS equation) 13
2.2.4 交換相關函數(Exchange-Correlation Function) 15
2.3 密度泛函理論-分子動力學（DFT-MD） 17
2.3.1 運動方程式 18
2.3.2 積分法則 19
2.3.3 時間步階選取 20
2.3.4 系綜(Ensemble) 21
2.3.5 Nosé-Hoover方法 22
2.4 原子級應力分析 24
2.5 分析方法 27
2.5.1 吸附能(Adsorption Energy) 27
2.5.2 Nudged elastic band (NEB)方法 28
2.5.3 原子距離變化量統計 30
第三章 結果與討論 31
3.1 鎢奈米線與奈米管幾何結構、機械性質與熱穩定性質分析 32
3.1.1 物理模型之建構 32
3.1.2 鎢奈米線與奈米管之機械性質 36
3.1.3 鎢奈米線與奈米管之熱穩定性質 41
3.2 鎢奈米線與奈米管電子性質之研究 46
3.3 CO在W奈米管及W(111)表面上的氧化性質研究 54
3.3.1 氧原子與氧分子吸附於W奈米管與W(111)表面的模型 54
3.3.2 W奈米管與W(111) 活性區域與表面吸附能分析 56
3.3.3 鎢奈米管氧化路徑分析 60
3.3.4 CO在W奈米管上氧化過程中PDOS分析 64
第四章 結論與建議 66
4.1 結論與建議 66
4.2 未來展望 67
參考文獻 68

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