Application of Periodic-Shell Boundary Condition to Non-Rigid Molecular Systems. Molecular Dynamics Simulations on a Flow around a Circular Cylinder.

Abstract

The present paper discusses the availability of the periodic shell boundary condition, which the author developed in the previous paper as an outer boundary condition for molecular dynamics simulations, to nonrigid molecular systems. For this purpose, we have conducted molecular dynamics simulations on a flow of Lennard-Jones liquids past a two dimensional circular cylinder. The ordinary boundary condition, i. e., the periodic boundary condition, gives significantly distorted velocity fields : for example, a flow near the boundary surfaces in the cylinder side direction flows along the boundary surfaces, namely, in the uniform flow direction ; the velocities near the boundary surfaces behind the cylinder are much larger compared to the results of the present boundary condition and Navier-Stokes equations ; a pair of vortices behind the circular cylinder are significantly distorted in the cylinder direction. On the other hand, the results of the present boundary condition agree well with those of Navier-Stokes equations qualitatively, and quantatively to a certain degree ; good agreement is obtained concerning the formation of a pair of vortices behind the circular cylinder and also concerning the flow fields in the side region of the cylinder. These results clearly show that the periodic-shell boundary condition is highly useful for non rigid molecular systems, and needless to say, for rigid molecular systems as well.