School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
J Chem Phys. 2017 Jul 14;147(2):024506. doi: 10.1063/1.4990029.
Non-equilibrium molecular-dynamics simulations of bulk methane clathrate hydrates have been conducted in a range of externally applied electromagnetic (e/m) fields. Studies into frequencies of system(or "global")-mass-density fluctuations showed that these clathrates have three major modes: the dominant one is attributable to water molecules' librations and occurs at 720 cm, regardless of any applied e/m fields. One of the more minor system-density fluctuations arises at 10-12 cm and is caused by the propagation of local-density fluctuations; again, this is independent of e/m fields. The final density fluctuation is caused by e/m fields, and it only becomes apparent for field strengths of 1.2 V/nm or higher. The frequency of this mode is always twice the frequency of the applied e/m field. It was shown that the main qualitative features of the translational and librational densities of states (DOSs) were unaffected by the application of e/m fields; however, a slight coupling effect was observed, producing a peak in all DOSs at the frequency of the applied field. This study showed that e/m fields below a certain intensity threshold do not lead to any marked structural distortion or dissociation effect on pre-existing bulk clathrates, in which the hydrogen-bonding structure of the lattice remains intact. This is verified by system-density and configurational-energy values as well as radial distribution functions.
已在一系列外部施加的电磁（e/m）场中对块状甲烷包合物水合物进行了非平衡分子动力学模拟。对系统（或“全局”）质量密度波动频率的研究表明，这些包合物有三种主要模式：主要模式归因于水分子的摆动，发生在 720 cm 处，与任何施加的 e/m 场无关。另一个较小的系统密度波动发生在 10-12 cm 处，是由局部密度波动的传播引起的；同样，这与 e/m 场无关。最后一种密度波动是由 e/m 场引起的，只有在 1.2 V/nm 或更高的场强下才会变得明显。该模式的频率始终是施加的 e/m 场频率的两倍。结果表明，施加 e/m 场不会影响平移和摆动态密度（DOS）的主要定性特征；然而，观察到了轻微的耦合效应，在所有 DOS 中产生了一个与施加场频率相对应的峰值。该研究表明，在一定强度阈值以下的 e/m 场不会导致预先存在的块状包合物发生任何明显的结构扭曲或离解效应，其中晶格的氢键结构保持完整。这通过系统密度和构型能量值以及径向分布函数得到了验证。
