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, coarsegrained 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/cm 3 , which is very close to the available experimental value of 1.008 g/cm 3 . 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.

High-entropy alloys (HEAs) break the design concept of traditional alloys and exhibit excellent mechanical properties. However, as a new member of the alloy family in recent years, the dependence of the deformation behavior of the HEAs on alloy composition and twin boundary (TB) is still unclear, and many phenomena urgently need to be revealed. Here, the effects of TB spacing and Ni concentration on the mechanical properties and deformation behavior of the nano-twinned (CoCrFeCu)1−XNiX HEA (nt-HEA) under tensile loading are investigated by molecular dynamics simulation. The results show that with the decrease in TB spacing, the average flow stress of the nt-HEA changes from Hall–Petch strengthening to inverse Hall–Petch softening. When the TB spacing is greater than a critical value, the plastic deformation mechanism is dominated by the slip of partial dislocations. However, when the TB spacing is less than the critical value, the plastic deformation mechanism is transformed into the formation of voids induced by the amorphous phase, which becomes the key factor for the softening of the nt-HEA. It is also found that the mechanical properties of the nt-HEA can also change from strengthening to softening by adjusting Ni concentration, which is closely related to the change of stacking fault energy of the nt-HEA. In addition, the plastic deformation mechanism and voids formation mechanism of the nt-HEA are also discussed in detail.

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