Large scale non-equilibrium molecular dynamic simulations

Author

Ravi K. Bhupathiraju

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Hank D. Cochran

Committee Members

Peter T. Cummings, Paul R. Bienkowski

Abstract

The massively parallel, distributed memory super-computers, with their highly scalable architectures, provide the most powerful route towards the realization of molecular simulations of realistic systems using current computer technology. In order to utilize the virtually unlimited power of the parallel computers, it is essential to develop efficient algorithms that scale with the computer. In this study we developed a parallel nonequilibrium molecular dynamics code to study the theological behavior of simple fluids over a wide range of shear rates. Large systems are especially necessary to obtain good statistical results at low reduced strain rates where the response of the system due to an applied shear field is weak compared to the thermal noise. The algorithm uses the domain decomposition technique with the link cells for parallelization. The SLLOD equations of motion with deforming cell boundary conditions were used for the shear flow simulations. A new modification to the deforming cell boundary conditions, namely, decreasing the angle at which the cell is realigned during deformation, has been proposed and was found to decrease the simulation time by almost half compared to the previous method. This efficient code, when run on the Intel's Paragon XP/S computers, allowed very large scale (up to 10⁶ particles) shear flow simulations of the Weeks-Chandler-Anderson (WCA) fluid to be carried out over four decades of reduced shear rates (10^-4-1.0). As expected the large system sizes did allow us to obtain statistically meaningful viscosity results at shear rates lower than those obtained in earlier studies and close to the experimentally obtainable shear rates. The viscosity results obtained from this study confirmed the onset of the Newtonian regime at low shear rates that was inferred in the earlier studies. The results were also consistent with the values obtained from transient time correlation functions and Green-Kubo relations.

Recommended Citation

Bhupathiraju, Ravi K., "Large scale non-equilibrium molecular dynamic simulations. " Master's Thesis, University of Tennessee, 1996.
https://trace.tennessee.edu/utk_gradthes/10771