Prediction of Optical and Dielectric Properties of 4‑Cyano-4-pentylbiphenyl Liquid Crystals by Molecular Dynamics Simulation, Coarse-Grained Dynamics Simulation, and Density Functional Theory Calculation

The Maier–Meier theory and Vuks theory were used to obtain the dielectric anisotropy and birefringence of the 4-cyano-4-pentylbiphenyl (5CB) liquid crystal system for a benchmark. The molecular dynamics (MD) simulation, coarse-grained molecular dynamics (CGMD) simulation, and the density functional theory (DFT) calculation were used to get the required parameters of the Maier–Meier theory and Vuks theory. The molecular density obtained by the MD simulation is about 1.05 g/cm3, which is very close to the available experimental value of 1.008 g/cm3. In the CGMD simulation, the order parameter is about 0.44 for the 5CB conformation at the temperature that the transformation from the nematic to disorder arrangement occurs. The polarizability (α), polarizability anisotropy (Δα), and dipole moment (μ) of a 5CB molecule were obtained by the DFT calculation with the functional of B3LYP/6-31+G­(2d,p). With these parameters, the birefringence of 5CB by the Vuks theory is very close to the experimental value with the error under 1%, but the dielectric constant and dielectric anisotropy by the Maier–Meier theory display the considerable errors higher than the corresponding experimental data by 218% and 260%, respectively. With the further concern about the Kirkwood’s correlation factor for the effective dipole moment, the dielectric constant and dielectric anisotropy errors decrease from 218% to 12% and from 260% to 2%, respectively. From these results, it shows the dielectric anisotropy and the birefringence of a liquid crystal system can be accurately predicted by the Maier–Meier theory and Vuks theory with the parameters from the MD, CGMD, and DFT calculation as well as considering the effective dipole moment.