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Structure and Dynamics of [PF$_6$][P$_{1,2,2,4}$] from Molecular Dynamics Simulations

Diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate, [PF$_6$][P$_{1,2,2,4}$], is an organic ionic plastic crystal with potential uses as a solid electrolyte in storage and light harvesting devices. In this work we present a molecular dynamics simulation study for this material covering an extended temperature range, from 175 K to 500 K. The simulations predicts a transition from the crystalline to a {\em semi} plastic phase at 197 K, the onset of cation jump-like rotations at 280 K, a third transition at 340 K to a {\em full} plastic phase and melting to 450 K. Overall, the simulations show a good agreement with the experimental findings providing a wealth of detail in the structural and dynamic properties of the system.