Molecular simulations can extend known literature data for numerous target fluids while utilizing force fields to model them accurately and realistically. Simulants, such as DMMP and DIMP have been studied using this approach [1,2]. Here, we model and characterize TEP based on the transferable potentials for phase equilibria (TraPPE). We use TraPPE descriptions of known organophosphates in literature and transfer their atom, bond, angle, and dihedral interaction parameters to TEP [2]. Additionally, ab initio calculations were performed to obtain the remaining parameters – dihedral interactions using potential energy scans, and partial charges [3]. To validate the model, we performed molecular dynamics (MD) simulations to predict the liquid densities and compared our predictions with available literature data [2,4,5]. Furthermore, Gibbs ensemble Monte Carlo simulations were performed to model vapor-liquid phase behavior. From these simulations, we compared the simulated vapor pressures to experimental values and calculated their critical parameters [6,7]. We also performed MD simulations to predict the enthalpy of vaporization, surface tension, viscosity and diffusivity. Moreover, we also parameterized and characterized trimethyl phosphate (TMP) due to its structural similarity to TEP.
Our study will help assess TEP and TMP as alternative CWA simulants, and provide predictions of their physical properties, i.e., liquid densities, vapor pressures, enthalpy of vaporization, surface tension, viscosity and diffusivity, in a wide range of temperatures.
Acknowledgements
This work was funded by the US Defense Threat Reduction Agency, through the University Research Alliance: Materials Science in Extreme Environments.
References
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