Molecular dynamics simulations of microwave effects on water using different long-range electrostatics methodologies

Non-equilibrium molecular dynamics (NEMD) simulations of water have been carried out in the presence of an external electromagnetic field of frequency 100 GHz and RMS intensity 0.1 V/Å in the isothermal–isobaric ensemble from 260 to 400 K and in the pure Newtonian case from ambient temperatures to the supercritical state. The rigid, non-polarizable SPC, SPC/E, TIP4P, TIP4P-Ew and the polarizable TIP4P-FQ potentials were used for a system of 256 molecules, along with both the Lekner and Ewald techniques to handle long-range electrostatics, in an effort to assess the impact of different long-range electrostatics methodologies on the results. Significant alterations in molecular mobility and hydrogen bonding patterns were found relative to zero-field conditions. The heating profiles were compared to that predicted from a macroscopic energy balance, and the TIP4P-FQ model was found to be superior in this aspect. Although the Lekner and Ewald techniques yielded similar results in the case of the non-polarizable potentials, some significant differences were noted between them for the TIP4P-FQ model at lower temperatures.