Thermal transport coefficients of liquid benzene by computer calculations

Abstract

Molecular-dynamics (MD) calculations with six-center Lennard-Jones potentials have been performed to model liquid benzene. Shear and bulk viscosity as well as thermal conductivity were determined for eight different states of liquid benzene. Agreement of experimental values and MD results is surprisingly good for the shear viscosity and the thermal conductivity. Even the strongly increasing shear viscosity of benzene near its triple point could be well reproduced by the MD computations. Bulk viscosity could not be compared with experiment. The calculated values are, however, expected to fall in line with measurable coefficients. In the wider neighborhood of the triple point of benzene, the time-correlation functions of the shear and the bulk viscosity begin to have an extreme form, namely, a decay to nearly zero in a short time range of only 0.3 ps followed by a positive branch of very small amplitude up to about 4 ps. This behavior of the time-correlation functions makes an accurate determination of the viscosities very difficult. MD runs of at least 0.6×${10}^6$ time steps are required for reliable computations. The molecule-number dependence of the results was found to be small, in agreement with previous findings. Systems of 32 molecules seem to be of satisfactory size.