## Research Abstracts Online

January
2008 - March 2009

### University of Minnesota Duluth

Swenson College of Science and Engineering

Department of Chemistry and Biochemistry

## PI: Paul D. Siders

### Molecular Dynamics Simulation of a Square-well Fluid Driven Upon a Square Lattice

The driven lattice gas (DLG) in two dimensions is a statistical-mechanical model for driven flow on a plane. The DLG model shows a transition to an anisotropic phase that is stabilized by the driving field. Monte Carlo simulation of related systems, a driven non-square lattice gas (previous work at MSI) and an off-lattice Lennard-Jones fluid, suggest that the phase transition in the DLG depends strongly on the square lattice and is not representative of off-lattice driven systems. This work explores a new model that can pass smoothly from a near-lattice-gas limit to an off-lattice fluid. To incorporate time-dependent dynamics, the new model is simulated with molecular dynamics rather than with Monte Carlo methods. To mimic a lattice gas’s nearest-neighbor attractions and single-site occupancy, the inter-particle potential is a square-well potential. The effect of the driving field’s strength on liquid-gas or fluid-fluid phase transitions is studied as a function of the strength of the underlying square lattice, which ranges from a nearly free square-well fluid to nearly the lattice gas. Preliminary results suggest that, when the lattice is strong, the field induces a conductive anisotropic phase similar to that observed in the DLG. On a lattice of zero strength, no strip-like conductive phase has yet been found, supporting others’ contention that a lattice is essential to striped conductive phases. Lattices of intermediate strength will probe the transition from DLG-like on-lattice behavior to streaming off-lattice behavior.