SHORT-TIME MOLECULAR ORIENTATIONAL DYNAMICS OF PCH5

We present results of a molecular dynamics simulation of the liquid cr ystalline substance p-n-pentyl-(p'-cyanophenyl)-cyclohexane (PCH5) wit hin a united atom force field approach and analyze in detail the behav ior of the orientational autocorrelation functions (CF's). Orientation al CF's are calculated for different sections within the molecule in t he 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 s trong non-exponentiality, observed in the short-time decay of experime ntally determined CF's for some mesogens originates from molecule flex ibility. Some proposals for model treatments of the internal rotation of mesogen molecules are also specified.