Dielectric relaxations of molten acetamide: dependence on the model interaction potentials and the effects of system size.

Molecular dynamics simulations of dielectric relaxations (DRs) in neat molten acetamide (CH3CONH2) at ~358 K have been carried out by employing two different versions of the OPLS force field parameters, namely, the OPLS-UA (united-atom) and the OPLS-AA (all-atom) model interactions. Three systems consisting of 250, 500, and 1000 molecules have been studied to examine the impact of system size on the simulated dielectric properties. A comparison between our simulation predictions and the experimental DR data in the MHz-GHz frequency regime reveals that the OPLS-UA interaction parameters better reproduce the experimental static dielectric constant, whereas the OPLS-AA interaction describes well the measured DR time constants. Moreover, a weak system size dependence has been observed. A Cole-Cole plot of the simulated and experimental dielectric spectra reveal non-Debye nature of liquid acetamide and corroborates well with the earlier observation on the collective single-particle reorientational relaxation of liquid acetamide. The simulated single dipole reorientation dynamics also reflects this weak non-Debye nature and reveals its contribution to the collective polarization relaxation. Simulation results obtained here set the right ground for investigating the colossal dielectric constant (~10⁶) of ionic acetamide deep eutectics reported earlier via DR measurements in the KHz-MHz regime. [ABSTRACT FROM AUTHOR]

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