Simulation studies of shear viscosity time correlation functions in liquidCS2

The Green-Kubo time correlation function for the shear viscosity in liquid CS2 has been simulated by molecular dynamics at several thermodynamic state points. The breakdown of this function into its kinetic and potential cont ributions as well as the cross-term between the two has been performed. Int ermolecular interactions were obtained from a three-centre atom-atom (12/6) Lennard-Jones potential model. The time correlation functions for the pote ntial part of the shear viscosity contain component two-, three- and four-b ody terms that were explicitly evaluated to show that they partially cancel each other at short times but at long times, they exhibit approximately ex ponential decays with magnitude ratios corresponding to nearly perfect canc ellation. In this respect, the correlation functions for CS2 resemble those of liquid argon. In addition, the microscopic stress tensor was separated into the portions arising from the repulsive and attractive branches of the Lennard-Jones model. This split gives rise to positive autocorrelation fun ctions involving the repulsive and the attractive forces plus a negative cr oss-correlation function between the two that partially cancels the contrib utions of the autocorrelation functions. It is argued that the breakdown of the potential part of the shear viscosity into its component parts is help ful in elucidating the role of molecular reorientation in determining the s eparate short and long time behaviours of this time correlation function fo r liquids such as CS2.