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本文基于第一性原理计算,对三种不同结构的Ⅰ型甲烷水合物进行弛豫,得到优化后的结构、电子态密度及光学性质,通过对结果的分析揭示不同笼子占据率对水合物的结构和相关性质的影响。这三种结构分别为:(cI)只有一个大笼未被占据;(cII)只有一个小笼未被占据;(cIII)每个笼子都被甲烷分子占据。结果显示,cIII是最稳定的,因为它有完美的晶体结构;cII和cI相对较不稳定,其中cI在缺失一个甲烷分子的情况下,结构出现了较大的变形,这导致它成为三种情况中最不稳定的结构;相反,同样缺失了一个甲烷分子的cII的结构变形就很小。cII和cI的体积变化分别是0.56%和2.1%,cII的电子态密度和能带几乎与cIII的一致,而cI的则与前两者差别很大。计算结果表明,相对于电子转移,质子无序对水合物的介电常数的影响更为主要;甲烷水合物只对紫外光有响应,无论结构和占据率差异如何,甲烷水合物都具有相近的光学性质。本文的结果证明,缺失一个甲烷分子,对cII造成的影响很小,其晶体结构、介电常数和光学性质与cIII的一致,然而同样缺失一个甲烷分子的cI的结构及性质却出现了巨大变化。这些结果可为水合物探测提供有价值的参考。 相似文献
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Grain size reduction of copper subjected to repetitive uniaxial compression combined with accumulative fold
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This paper reports a novel method of repetitive uniaxial compression
combined with accumulative fold for preparing bulk submicron- to
nanocrystalline copper starting with a coarse grained counterpart.
Grain size reduction and microstrain variations of the high purity
copper samples after different passes of compression and fold are
investigated by scanning electron microscope and x-ray diffraction
(XRD), respectively. Our results show that the average grain size of
samples decreases from about 830nm to 127nm as the number of
compression passes increases to 30. Microstrain in the compressed
sample is found to increase for the first 20 passes, but to decrease at
the last 10 passes. The variations of compressive yield strength and
the shift of XRD peaks to larger diffraction angles are observed in
the squeezed sample. Our experimental results demonstrate that the
repetitive uniaxial compression combined with accumulative fold is
an effective method to prepare bulk nanocrystalline metallic
materials, in particular for soft metals such as Cu, Al and Pb. 相似文献
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