Pressure-viscosity relation of 2,2,4-trimethylhexane predicted using all-atom TEAM force field

Abstract

The pressure-dependent viscosity of 2,2,4-trimethylhexane is predicted using all-atom TEAM force field and the non-equilibrium periodic perturbation (PP) method. The viscosities predicted using the PP method do not show Newtonian plateau in the precision range of prediction for high-viscosity fluids. Using four alkane molecules as test cases, we found that our previously published force field, developed for ambient pressure conditions, is inaccurate for predicting viscosities under elevated pressures. Two approaches were attempted to enhance the pressure transferability of the force field: one involves moving the non-bond interaction site of hydrogen closer to that of attached carbon, which smooths the van der Waals (vdW) surface of molecule, and the other involves replacing the LJ-12-6 function by LJ-9-6, making the repulsion softer. Both approaches enhanced the pressure transferability; however, the former works well below 500 MPa, while the latter is valid under pressures up to 1 GPa.