MODIFIED NONEQUILIBRIUM MOLECULAR-DYNAMICS FOR FLUID-FLOWS WITH ENERGY-CONSERVATION

The nonequilibrium molecular dynamics generated by the SLLOD algorithm [so called due to its association with the DOLLS tensor algorithm (D. J. Evans and G. P. Morriss, Statistical Mechanics of Nonequilibrium L iquids (Academic, New York, 1990)] for fluid flow is considered. It is shown that, in the absence of time-dependent boundary conditions (e.g ., shearing boundary conditions via explicit cell dynamics or Lees-Edw ards boundary conditions), a conserved energy, H' exists for the equat ions of motion. The phase space distribution generated by SLLOD dynami cs can be explicitly derived from H'. In the case of a fluid confined between two immobile boundaries undergoing planar Couette flow, the ph ase space distribution predicts a linear velocity profile, a fact whic h suggests the flow is field driven rather than boundary driven. For a general flow in the absence of time-dependent boundaries, it is shown that the SLLOD equations are no longer canonical in the laboratory mo menta, and a modified form of the SLLOD dynamics is presented which is valid arbitrarily far from equilibrium for boundary conditions approp riate to the flow. From an analysis of the conserved energy for the ne w SLLOD equations in the absence of time-dependent boundary conditions , it is shown that the correct local thermodynamics is obtained. In ad dition, the idea of coupling each degree of freedom in the system to a Nose-Hoover chain thermostat is presented as a means of efficiently g enerating the phase space distribution. (C) 1997 American Institute of Physics.