Soret coefficients and mass diffusion coefficients of three states of the n-pentane–n-decane mixture have been measured by thermal diffusion forced Rayleigh scattering (TDFRS) and are compared with molecular dynamics simulations values. Both equilibrium (EMD), synthetic (S-NEMD), and boundary driven (BD-NEMD) nonequilibrium techniques have been applied to compute the phenomenological and the transport coefficients relevant to the Soret effect. It is found that statistical error on cross-coefficients using equilibrium and dynamical S-NEMD is too high to enable any comparison with experiments, whereas stationary S-NEMD and BD-NEMD methods have statistical error less than ≈35%. S-NEMD simulations have been carried out in the center-of-mass reference frame and the resulting transport coefficients transformed to the center-of-volume frame of reference. The mass diffusion coefficients are sensibly affected by this transformation and show the same weight fraction dependence as the experimental value, although a difference of roughly a factor of 1.4 is found. The Soret coefficients are, as expected, unaffected by the frame of reference transformation and a good agreement between experiment and simulations is found.

The Soret and the other transport coefficients, characterizing the heat and mass transport in binary mixtures, have been obtained by equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively). Two state points of the argon-krypton mixture are considered, for which experimental values of the Soret coefficient are available. To attempt a comparison between simulations and experiments the common enthalpy-diffusion-free expression for the heat flux has been chosen. The comparison of the simulations with the experiments shows a remarkable agreement, for all the several utilized EMD and NEMD techniques (dynamical and stationary). The techniques, used over 0.3 micros of total simulation time span, are slow convergent but have comparable performances.

We present results of a standard (constant energy) molecular dynamics simulation of a Lennard-Jones lattice at low temperature. The kinetic energy fluctuations exhibit an anomalous behavior, due to a dynamics which is only weakly chaotic. Such a dynamics does not allow the use of the usual microcanonical equilibrium formula to compute the specific heat. We devise a different method for computing the specific heat, which exploits just the weak chaos at low temperature. The result is that at low temperature this “revisited” specific heat is lower than the classical value, and approaches zero when the temperature goes to zero. Only for exceedingly long trajectories does the specific heat approach the classical value, with the exception of the very low temperature range. These results prompt a reconsideration, in the frame of modern nonlinear dynamics, of early intuitions by Nernst and Jeans