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Reliable Viscosity Calculation from High-Pressure Equilibrium Molecular Dynamics: Case Study of 2,2,4-Trimethylhexane
Gözdenur Toraman1, Dieter Fauconnier1,2, Toon Verstraelen3
1Soete Laboratory, Ghent University, Technologiepark-Zwijnaarde 46, 9052 Ghent, Belgium.
Journal of Chemical Theory and Computation
|July 27, 2026
Summary
We improved viscosity calculations using the STable AutoCorrelation Integral Estimator (STACIE) algorithm. Our enhanced method accurately predicts lubricant viscosity under high pressure, overcoming limitations of previous simulation techniques.
Area of Science:
- Materials Science
- Computational Chemistry
- Physical Chemistry
Background:
- Viscosity is crucial for liquid lubricants but difficult to measure accurately at high pressures.
- Equilibrium molecular dynamics (EMD) simulations offer an alternative to experiments but face challenges in time sufficiency and uncertainty quantification.
- Existing methods using Green-Kubo formalism can be limited by finite trajectory data.
Purpose of the Study:
- To enhance the STable AutoCorrelation Integral Estimator (STACIE) algorithm for more accurate viscosity determination.
- To address practical challenges in EMD simulations for transport property estimation.
- To improve the reliability and accuracy of shear viscosity predictions under high pressure.
Main Methods:
- Extended STACIE by incorporating the Lorentz model for viscosity and correlation time estimation from pressure fluctuation spectra.
- Supplemented conventional pressure tensor elements with additional uncorrelated components for shear viscosity calculations.
- Applied the enhanced STACIE to calculate the shear viscosity of 2,2,4-trimethylhexane using EMD simulations up to 1 GPa.
Main Results:
- Demonstrated STACIE's capability for reliable high-pressure viscosity calculations with validated uncertainty quantification.
- Achieved viscosity estimates with less than 4% relative error compared to experimental results up to 1 GPa.
- Identified insufficient simulation times and ad hoc postprocessing as primary sources of error in previous studies.
Conclusions:
- The enhanced STACIE provides a robust and automated solution for accurate viscosity predictions in liquid lubricants.
- Accurate viscosity prediction under high pressure is achievable with sufficient simulation times and systematic computational approaches.
- The study highlights the importance of methodological rigor in EMD simulations for reliable material property determination.
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