Theory and simulation of chain-molecule fluid structure

Results of NVT molecular-dynamics simulations are reported for modelled n-butane and n-pentane over a range of densities at temperatures of about 430 K. The model potential is the repulsive part of the Lennard-Jones potential with bond angles constrained at 109-47° and bond lengths of 0153nm, where σ= 0-3923 nm and e/k = 72 K. Simulation results for average site-site distribution functions are compared with results of an approximate RISM theory. Similarly to the case of diatomic fluids, the accuracy of the approximate theory is only qualitative, but trends of key features of the fluid structure are well represented. The softness of the Lennard-Jones potential appears to play a significant role in smoothing away several potential sources of error in the approximate theory.