Comparative study of local structure of two cyanobiphenyl liquid crystals by molecular dynamics method.

Fully-atomistic molecular dynamics simulations were carried out on two similar cyanobiphenyl nematogens, HO-6OCB and 7OCB, in order to study effects of hydrogen bonds on local structure of liquid crystals. Comparable length of these two molecules provides more evident results on the effects of hydrogen bonding. The analysis of radial and cylindrical distribution functions clearly shows the differences in local structure of two mesogens. The simulations showed that anti-parallel alignment is preferable for the HO-6OCB. Hydrogen bonds between OH-groups are observed for 51% of HO-6OCB molecules, while hydrogen bonding between CN- and OH-groups occurs only for 16% of molecules. The lifetimes of H-bonds differ due to different mobility of molecular fragments (50 ps for N⋅⋅⋅H-O and 41 ps for O⋅⋅⋅H-O). Although the standard Optimized Potentials for Liquid Simulations - All-Atom force field cannot reproduce some experimental parameters quantitatively (order parameters are overestimated, diffusion coefficients are not reproduced well), the comparison of relative simulated results for the pair of mesogens is nevertheless consistent with the same relative experimental parameters. Thus, the comparative study of simulated and experimental results for the pair of similar liquid crystals still can be assumed plausible.