The Enskog-type theory of the velocity autocorrelations in the two-dimensional nematic of hard needles

As it was shown from molecular dynamics of two-dimensional hard needles [Phys. Rev. E 66, 012201 (2002)], the uniaxial velocity autocorrelation function (VACF) of this system exhibits a two time scale character. This corresponds to the symmetry of the particles. In this paper we provide a theory of the Enskog type that corroborates the idea that the VACF can be successfully described as a sum of two single decays. From the comparison between molecular dynamics and theoretical results, we show that the Enskog approach is a satisfactory kinetic theory, which functions as well in the nematic as in the isotropic phase. Different properties of VACFs have been investigated, in particular, the dependence on the orientational order, temperature, and particles' inertness. (C) 2004 American Institute of Physics.