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 fieldparameters, namely, the OPLS-UA (united-atom) and the OPLS-AA (all-atom) model interactions. Threesystems consisting of 250, 500, and 1000 molecules have been studied to examine the impact of system sizeon the simulated dielectric properties. A comparison between our simulation predictions and the experimentalDR data in the MHz-GHz frequency regime reveals that the OPLS-UA interaction parameters betterreproduce the experimental static dielectric constant, whereas the OPLS-AA interaction describes well themeasured DR time constants. Moreover, a weak system size dependence has been observed. A Cole-Cole plotof the simulated and experimental dielectric spectra reveal non-Debye nature of liquid acetamide and corroborateswell with the earlier observation on the collective single-particle reorientational relaxation of liquidacetamide. The simulated single dipole reorientation dynamics also reflects this weak non-Debye nature andreveals its contribution to the collective polarization relaxation. Simulation results obtained here set the rightground for investigating the colossal dielectric constant (~106) of ionic acetamide deep eutectics reportedearlier via DR measurements in the KHz-MHz regime.
Volume 133, 2021
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