A correlation-length of density fluctuations around the critical point is very small, and the influence of microscopic factors such as molecular structure may not be neglected. However, there have been few systematic studies of the effect of molecular structure on the density fluctuations around the critical point. In this study, we performed microscopic analyses using molecular dynamics (MD) simulations and macroscopic analyses using equation of states (EOS) for 2-Center-Lennard-Jones (2CLJ) fluids in supercritical conditions around each critical point to investigate the effect of molecular structure on the density fluctuation. Diatomic fluids with different internuclear distances below the atomic diameter were analyzed, and the static structure of density fluctuations was compared for investigating the effect of molecular anisotropy. The results show that in the microscopic analysis, the effect of the molecular structure is manifested in the low wavenumber region (100~500Å in real space), and the density fluctuation is suppressed in a diatomic fluid with a larger inter-nuclear distance. The same trend is also confirmed in the density fluctuations calculated from EOS, showing that the present MD results are qualitatively consistent with the macroscopic results.
SHIGEMURA et al. (Wed,) studied this question.