單壁奈米碳管彈力性質之分子動力學模擬

Abstract

在此篇論文中，使用分子動力學(molecular dynamics)模擬單壁奈米碳管軸向的拉伸和壓縮，藉由求出系統總能量和應變的關係來得到碳管的楊氏模量(Young’s modulus)，碳和碳間所使用的勢能為緊束縛勢能(Tight-Binding potential)及特索夫勢能(Tersoff potential)。探討的主要參數為碳管的長度、直徑比。考慮的情況有兩種，一為固定直徑，改變長度，另一種為固定長度，改變直徑。比較不同長度、直徑比與楊氏模量的關係。計算結果得到在Tight-Binding potential下，單壁奈米碳管的楊氏模量為0.989 TPa。Tersoff potential所得的模量為0.681 TPa。兩種勢能的結果皆顯示單壁奈米碳管的楊氏模量隨長徑比減小而增加。在挫曲發生時的軸向應變值，緊束縛勢能及特索夫勢能的值分別為20%及12%。模擬結果也顯示(17,17)直徑為1.144 nm的碳管已無法維持圓形截面。

The aim of this thesis is to focus on using the molecular dynamics (MD) simulation to simulate the axial deformation of a single-walled carbon nanotube. In this thesis, we select Tight-Binding potential and Tersoff potential to represent the interactions between carbons of nanotube. The Young’s modulus was calculated by using the energy versus strain relation. In addition, the effect of diameter of tube is discussed in this article. The simulation shows the average of Young’s modulus under two different potential situations. One is 0.989 TPa through the Tight-Binding potential, and the other is 0.681 TPa through the Tersoff potential. The result of the two potentials demonstrates that there will be a rise in the Young’s module when aspect ratio is decreased. Further, the critical buckling strain are 0.20 and 0.12 through the Tight-Binding potential and the Tersoff potential, respectively. The cross section of the single-walled carbon nanotube is not circular any more when the diameter is 1.144 nm in the simulation.