Configurations of 200 p-n-pentyl-(p-cyanophenyl)-cyclohexane (PCHS) molecules from molecular dynamics simulations were used to calculate the Rayleigh light scattering spectra of the isotropic phase. The interaction induced contribution is calculated to the first order dipole-induced dipole terms in the point molecular polarizability approximation. The effect of the size of the simulated system is checked from different points of view. Molecular flexibility is explicitly taken into account and comparisons in terms of time correlation functions are performed. In contrast to systems of small-sized molecules no cancellation effect is observed for the interaction induced contribution to the scattered light intensities of this mesogen. Studies of the different contributions induced by the isotropic and the anisotropic part of the molecular polarizability, evidenced the negligibility of the second one and showed the importance of orientational-translational intermolecular correlations for spectra formation in mesogen systems. The problem of comparing anisotropic and isotropic components of Rayleigh spectra is outlined.