【作者】 叶翔；

【导师】 龚新高；

【作者基本信息】 复旦大学 ， 理论物理， 2007， 博士

【摘要】 本文通过使用分子动力学方法研究了纳米材料多壁碳纳米管和硒化镉团簇在外压下的结构相变行为，以及基于碳纳米管基础上的储氢容器。主要研究内容可以概括为以下几部分：第一，研究了外加压强下(10，10)@(15，15)，(9，9)@(14，14)，(8，8)@(13，13)，(7，7)@(12，12)及(6，6)@(11，11)五种公度匹配的扶手椅型双壁碳纳米管的结构相交。我们发现在一定压强下，这些碳纳米管都会发生管口截面从圆形转变到椭圆型的结构相变，这个相变压强主要由内管的大小决定。同时我们的计算结果表明碳管键长在相变后会突然变长，我们采用了一个简单的弹性模型来解释这一物理现象。第二，研究了多壁碳纳米管在外压下的径向压力传递。结果表明外管对内管起到一个保护作用，使内管感受到的压强远远小于外压。我们发现径向压力传递系数主要由碳纳米管的大小及管间的结构匹配决定。同时我们提出了一个测量多壁碳纳米管径向压力传递系数的实验方法。第三，研究了碳纳米管的抗内压性能，并在此基础上设计了一种纳米储氢容器。计算结果表明在2.5GPa的压强下这种容器的储氢效率可以达到7.7％。第四，我们使用等压分子动力学的方法研究了硒化镉团簇在外压下的结构相变。我们发现硒化镉团簇的结构相变与其自身的大小及形状密切相关。计算结果表明球形纳米团簇的相变压强是随团簇的增大而逐渐减小的。在所有研究的多面体团簇相变后都是形成无缺陷的石盐结构，而球形团簇相变后的结构都是多晶界的。另外在论文的第一章里简要介绍了碳纳米管材料的发现历史及一般性质，硒化镉团簇的研究背景。在第二章中对本论文所使用的分子动力学力方法作了介绍，包括该方法的基本概念、原子势函数以及不同的等温及等压分子动力学方法。更多还原

【Abstract】 In this thesis we have studied the pressure-induced structure transition of multiwalled carbon nanotube and CdSe nanocrystal by using constant pressure molecular dynamics simulations. And we have designed a nanocontainer for the storage of hydrogen based on the carbon nanotube.First, we have studied the structure of isolated DWCNTs under external pressure. We find that pressure-induced structure transition takes place in all the studied DWCNTs. The critical transition pressure is strongly dependent on the radius of the inner tube. The bond length of the carbon nanotube would increase after phase transition, and we use a elastic model to explain this physics phenomenon.Second, the radial pressure transmission behavior of MWCNTs is studied. It is found that the response pressure of inner tube is much lower than the external pressure before structural transition happens. The pressure transmission efficiency increases with tube radius. Meanwhile the pressure transmission efficiency also depends upon morphology combination of MWCNTs. With the same size, the pressure transmission efficiency of commensurate MWCNTs is higher than that of incommensurate ones. Based on the simulation results, we propose an experimental method to determine the pressure transmission efficiency of MWCNTs.Third, we have studied the possibility of carbon nanotube acting as high pressure container. Based on the results, we designed a nano-container for the storage of hydrogen. At 2.5 GPa, the storage weight ratio of the container approaches a promising 7.7%. Fourth, the structural transformation of CdSe nanocrystals under hydrostatic pressure is studied. We have found the structural transformation of CdSe nanocrystal is highly affected by the size and shape. The results show that the pressure for WZ to RS structural transformation of spherical nanocrystal decreases with nanocrystal size, while it seems to increase for facet one. For all spherical nanocrystals, the final structures have nano scale grain boundaries. All the faceted ones undergo uniform deformation, the transformed RS structure is of single domain nanocrystal.更多还原