Molecular Dynamics Studies of Liquid and Chain Systems
Molecular Dynamics simulation has been used for the past 20 - 30 years to study interfacial properties of liquids though the foundations for these studies were laid as far back as 1791 when the astronomer Joseph Dalambre used the time reversible algorithm, commonly called the Verlet algorithm, for the integration of Newton's equations. Some of the properties obtained from Molecular Dynamics, commonly called MD, simulation are density profiles, system configurations, as well as stress or pressure tensor profiles. Generally, the surface tension has been calculated by integrating the stress tensor profile over the width of the interfacial region. In an effort to circumvent the stress tensor calculation and the technical difficulties associated with extensions to include many-body interactions, I will study the feasibility of implementing an equality recently developed by C. Jarzynski to determine the equilibrium surface free energy and, subsequently, the surface tension of an immiscible L-J fluid from an ensemble average of a set of non-equilibrium simulations. In addition to exploring suitable systems for this study, we explore relative computational efficiency of the second method. We also compare the equilibrium free energy difference computed by the Jarzynski method to the apparent free energy difference computed by the Irving-Kirkwood (IK1) approach. We conclude first that both the Jarzynski and IK1 approaches can be useful tools in simulating immiscible liquid systems. The Jarzynski relation is quite effective at extracting free energy differences associated with interfacial area changes in systems comprised of closely spaced, interacting interfaces. For isolated interfaces, the IK1 method is still the best approach for obtaining interfacial tension. We also find that a fast switching Jarzynski algorithm is as efficient and much less costly to implement than a slow switching method.
Advisor:Julia Thompson; Jeremy Levy; Rainer Johnsen; Yadin Y. Goldschmidt; Robert Coalson; Steven Dytman
School:University of Pittsburgh
School Location:USA - Pennsylvania
Source Type:Master's Thesis
Date of Publication:10/05/2004