Nature of intrinsic uncertainties in equilibrium molecular dynamics estimation of shear viscosity for simple and complex fluids
Abstract
We study two types of intrinsic uncertainties, statistical errors and system size effects, in estimating shear viscosity via equilibrium molecular dynamics simulations, and compare them with the corresponding uncertainties in evaluating the self-diffusion coefficient. Uncertainty quantification formulas for the statistical errors in the shear-stress autocorrelation function and shear viscosity are obtained under the assumption that shear stress follows a Gaussian process. Analyses of simulation results for simple and complex fluids reveal that the Gaussianity is more pronounced in the shear-stress process (related to shear viscosity estimation) compared with the velocity process of an individual molecule (related to self-diffusion coefficient). At relatively high densities corresponding to a liquid state, we observe that the shear viscosity exhibits complex size-dependent behavior unless the system is larger than a certain length scale, and beyond which, reliable shear viscosity values are obtained without any noticeable scaling behavior with respect to the system size. We verify that this size-dependent behavior is configurational and relate the characteristic length scale to the shear-stress correlation length.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jul 28, 2018
- Source ID
- 10.1063/1.5035119
Entities
People
- Changho Kim
- Eok Kyun Lee
- George Karniadakis
- Kang-sahn Kim
- Myung Hoon Han
- Zhen Li
Organizations
- Brown University
- KAIST
- Lawrence Berkeley National Laboratory
- United States Army Research Laboratory
- United States Department of Energy