We present results of a molecular dynamics simulation of the liquid crystalline substance p-n-pentyl-(p’-cyanophenyl)-cyclohexane (PCH5) within a united atom force field approach and analyze in detail the behavior of the orientational autocorrelation functions (CF’s). Orientational CF’s are calculated for different sections within the molecule in the frame of the nematic director and in the internal frame. Comparison with autocorrelation functions of the torque acting on the molecules and cross-correlation factors have led us to the conclusion that the strong non-exponentiality, observed in the short-time decay of experimentally determined CF’s for some mesogens originates from molecule flexibility. Some proposals for model treatments of the internal rotation of mesogen molecules are also specified.