A new algorithm for unrestricted duration nonequilibrium molecular dynamics simulations of planar elongational flow

We apply the spatially and temporally periodic boundary conditions devised by Kraynik and Reinelt (Int. J. Multiphase Flow 18 (1992) 1045) to an atomi c fluid undergoing planar elongational flow and describe several algorithms which efficiently apply the required nonstandard periodic boundary conditi ons. These periodic boundary conditions guarantee unrestricted simulation t imes, and are simply implemented if a rotational transformation is first ap plied to the coordinates of all atoms such that one of the cell boundaries aligns with the direction of elongation. While in the transformed frame one can apply either Lagrangian rhomboid (LR) or "deforming brick" (DB) period ic boundary conditions to all particle coordinates and relative distances. The latter (DB) scheme turns out to be very similar in form to standard Lee s-Edwards periodic boundary conditions for planar shear flow, and both the LR and DB schemes are shown to be equivalent and numerically highly efficie nt. (C) 1999 Elsevier Science B.V.