Enhancing NEMD with automatic shear rate sampling to model viscosity and correction of systematic errors in modelling density: Application to linear and light branched alkanes

TL;DR

This paper introduces an automatic shear rate sampling algorithm for NEMD simulations to accurately model viscosity and correct systematic errors in density modeling for alkanes, demonstrating improved agreement with experimental data.

Contribution

It presents a novel sampling algorithm for shear rates in NEMD and applies correction methods to improve density and viscosity predictions in molecular simulations.

Findings

Density modeling achieves an average deviation of 3.4 g/l at 25°C.

Viscosity predictions show an average deviation of -1%.

The sampling algorithm enhances viscosity simulation accuracy.

Abstract

We perform molecular dynamics simulations to model density as a function of temperature for 74 alkanes with 5 to 10 carbon atoms and non-equilibrium molecular dynamics simulations in the NVT ensemble to model kinematic viscosity of 10 linear alkanes as a function of molecular weight, pressure, and temperature. To model density, we perform simulations in the NPT ensemble before applying correction factors to exploit the systematic error in the SciPCFF force field, and compare results to experimental values, obtaining an average absolute deviation of 3.4g/l at 25 $^{\circ}$ C and of 7.2g/l at 100 $^{\circ}$ C. We develop a sampling algorithm that automatically selects good shear rates at which to perform viscosity simulations in the NVT ensemble and use Carreau model with weighted least squares regression to extrapolate Newtonian viscosity. Viscosity simulations are performed at experimental densities and show an excellent agreement with experimental viscosities, with an average percent deviation of -1% and an average absolute percent deviation of 5%. Future plans to study and apply the sampling algorithm are outlined.