Molecular-dynamics simulation of methane-hydrate crystallisation in terahertz electromagnetic fields: Assessment of field intensities

Non-equilibrium molecular dynamics simulations were conducted to study the growth and dissolution of a spherical methane hydrate crystallite, using a polarizable water potential, encircled by a liquid phase of saturated water and methane, both in the microwave to far-infrared range and under applied external electromagnetic (e/m) fields (5 GHz to 7.5 THz) at r.m.s. electric-field strengths of up to the order of 1 V·nm⁻¹ — in an attempt to assess and model the “threshold” field intensities required to initiate hydrate dissolution. The average growth rate of the crystallite in the absence of a field was found to be approximately 0.32 water and 0.045 methane molecules per picosecond. Upon applying e/m fields, deviations from zero-field crystal growth patterns were observed for r.m.s. field strengths, especially at ∼ 1 V·nm⁻¹ as a rough ‘threshold’. When the water dipole was aligned with the external field, systematic frequency variations were observed, providing a mechanistic rationale for field-coupling effects on dipole direction/magnitude and hydrogen-bonding shifts.