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虽然水分子结构简单, 但是关于水冰的基本理论仍有很多问题没有科学答案. 对于冰的原子分子振动, 人们对其分子内的伸缩和弯曲振动以及分子的空间转动已经研究得很清楚. 然而30年前, 高亮度的非弹中子散射实验发现, 很多冰相的远红外分子平移区中存在两个明显的特征振动峰, 对其来源一直没有定论. 本文基于第一性原理密度泛函理论的CASTEP代码, 系统研究了不同冰相的振动谱和振动模式. 在对最简单的氢有序冰Ic模型的研究中, 首次发现了两类本征的氢键振动模式. 以此为线索, 继续模拟其他的冰相, 发现无论是氢有序还是氢无序结构都存在这个规律. 利用冰晶格局域正四面体理想模型, 理论上证明了两类振动模式可分为围绕一个水分子的氢键的四键振动和双键振动. 高压下, 因为结构变形, 存在介于二者之间的耦合振动. 此外, 还有能量更低的一些光学支振动模式, 比如团簇的振动、面间振动. 冰VII/VIII, XV/VI等结构, 是由两个子晶格嵌套而成的, 两个子晶格之间还有非氢键的相对振动. 综上, 这些分子平移振动可解释所有冰相的远红外振动谱, 为冰的分子振动理论补足了最后一块拼图. 由于液态水不存在这两类氢键振动, 因此其远红外吸收带在两个氢键位置恰好是个波谷. 结合太赫兹激光技术的发展, 此理论有望在工业除冰、食品解冻、可燃冰开采和生物分子冷冻塑型等领域产生系列原创成果.Despite its simple molecular structure, water is still a mystery to scientists. For the atomic and molecular vibrational modes of ice, as is well known, there are two kinds of vibrations: intra-molecular O—H stretching vibration and H—O—H bending vibration within the molecules and three kinds of molecular spatial rotations. However, thirty years ago, a high flux inelastic neutron scattering experiment showed that there are two distinct characteristic peaks in the far-infrared molecular translational vibration region of many ice phases. The origins of these peaks have not been determined till now. In this work, based on the CASTEP code, a first-principles density functional theory plane wave programme, the vibrational spectra as well as the vibrational normal modes of a series of ice phases are investigated. Two kinds of intrinsic hydrogen bond vibrational modes are first found in hydrogen-ordered ice Ic. Then it is found to be a general rule among ice family. Based on the ideal model, we prove that the two vibrational modes can be classified as four-bond vibration and two-bond vibration. There are many coupling modes in-between due to tetrahedral structure deformation under high pressure. Besides, there are also some optical vibrational modes with lower energy in the translational region, such as cluster vibrations and inter-plane vibrations. In Ice VII/VIII and XV/VI, each of which consists of two sublattices, there exist non-hydrogen bond vibrations. These molecular translational vibrations can explain all the far-infrared vibrational spectrum of ice phase, which makes up the last piece of the jigsaw puzzle for the molecular vibration theory of ice. The two vibrational modes do not exist in liquid water due to the collapse of the rigid tetrahedral structure. Thus, a window remains for ice resonance absorption with minimum energy loss in water. This theory is expected to be applicable to industrial deicing, food thawing, gas hydrate mining, and biomolecule frozen molding, etc.
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Keywords:
- ice/
- hydrogen bond/
- vibration mode/
- density functional theory
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Ice phase Environmental pressure/GPa Energy cutoff/eV K-mesh or seperation Ih 0 830 3 × 2 × 2 Ic 0 1200 7 × 7 × 8 II 0.50 750 2 × 2 × 2 V 1.00 750 2 × 2 × 1 VI 2.00 750 2 × 2 × 2 VII 2.40 830 3 × 3 × 2 VIII 2.40 1000 4 × 4 × 5 IX 0.30 750 2 × 2 × 2 X 120.00 830 0.07/Å XI 0 750 6 × 6 × 3 XIII 1.00 830 2 × 3 × 1 XIV 0.55 750 2 × 2 × 3 XV 0.90 750 4 × 4 × 4 XVI 0 750 1 × 1 × 1 XVII 0.40 830 1 × 1 × 1 
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ICE H···O O—H O—H···O HOH Angle Translation Libration Bending Stretching Density Ice X 1.138 1.138 2.275 109.5 — — — — 3.3 Ice VIII 2.038 0.976 3.013 105.1 161-254 502-1032 1589-1742 3357-3480 1.42 Ice XIII 1.786–3.173 0.980–0.987 2.751–2.874 102.7–108.1 50–318 524–982 1629–1721 3198–3441 1.18 Ice XV 1.902–1.991 0.978–0.981 2.886–2.908 101.6–107.2 73–285 477–936 1609–1709 3278–3485 1.21 Ice XIV 1.986–1.838 0.978–0.984 2.793–2.951 102.8–105.3 104–292 502–933 1647–1735 3234–3478 1.15 Ice II 1.815–2.057 0.976–0.986 2.796–3.023 102.8/105.0 142–318 522–969 1659–1723 3193–3483 1.06 Ice IX 1.829–1.849 0.984/0.985 2.802–2.824 104.2/104.7 67–307 580–1003 1639–1716 3177–3391 1.01 Ice Ic 1.799 1.000 2.798 105.6 230/321 589–1053 1631–1708 3113–3334 0.89 Ice XI 1.813/1.814 0.987/0.988 2.799/2.802 105.7/106.0 47–310 586–1063 1634–1710 3110–3353 0.89 Ice Ih 1.788–1.866 0.986–0.989 2.784–2.843 104.7–106.2 33–327 579–1030 1651–1706 3110–3363 0.88 XVII 1.806–1.840 0.986–0.988 2.791–2.826 105.0–107.9 36–301 588–1037 1635–1709 3125–3369 0.81 XVI 1.797–1.845 0.984–0.990 2.768–2.830 105.1–106.3 53–315 594–1053 1649–1715 3117–3380 0.80 下载:
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