Structure and stability of water chain in a carbon nanotube
Structure and stability of water chain in a carbon nanotube
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DOI：
10.1088/0953-8984/20/01/015213
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发表时间：
2008-01
期刊：
影响因子：
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通讯作者：
I. Hanasaki;A. Nakamura;Toru Yonebayashi;S. Kawano
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文献类型：
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作者：
I. Hanasaki;A. Nakamura;Toru Yonebayashi;S. Kawano
水分子在(6，6)碳纳米管中形成单一的链状结构，这种稳定性不同于更大直径的碳纳米管中的水分子，更不用说块体碳纳米管了。利用分子动力学(MD)方法和量子力学(QM)计算，我们研究了集体结构和氢键行为与密度相关的特征。分子动力学实验结果表明，水密度越高，氢键寿命越长。另一方面，氢键寿命并不随密度的降低而显著降低，但当密度低于某一临界值时，氢键寿命基本保持不变。水分子的平均取向角由水偶极矩和碳纳米管轴的夹角定义，密度越高，分子的平均取向角越小，密度越低，分子取向角越接近33°。这种结构和稳定性的渐近性质源于水分子的不均匀分布。用密度泛函理论进行QM计算得到的平均取向角与MD的结果相吻合。量子化学分析还表明，水在碳纳米管中的电荷分布源于空间受限的分子构型，而不是水与碳纳米管之间的强电子相互作用。
Water molecules form a single-file chain structure in a (6, 6) carbon nanotube (CNT), and this stability is different from that of water molecules confined in CNTs with larger diameters, let alone the bulk. Using the molecular dynamics (MD) method and quantum mechanical (QM) calculations, we investigate the characteristics in the context of density dependence of the collective structure and hydrogen bond behavior. The results obtained from MD show that high water density leads to substantially longer hydrogen bond lifetimes. On the other hand, the hydrogen bond lifetime does not noticeably decrease with decreasing density but remains roughly the same when the density is lower than a certain critical value. The mean molecular orientation angle of the water molecule, defined by the angle that comprises the water dipole moment and the CNT axis, is smaller for higher densities, and asymptotically approaches 33° on the low density side. Such an asymptotic nature of the structure and stability stems from non-uniform distribution of water molecules. The mean orientation angle obtained from QM calculations using density functional theory coincides with the MD result. QM analysis also suggests that the charge distribution of water in the CNT originates from the molecular configuration due to spatial confinement rather than strong electronic interaction between water and the CNT.