Global-density fluctuations in methane clathrate hydrates in externally applied electromagnetic fields.

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-1, regardless of any applied e/m fields. One of the more minor system-density fluctuations arises at 10-12 cm-1 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.