An Atomistic Simulation for 4-Cyano-4′-pentylbiphenyl and Its Homologue with a Reoptimized Force Field

Abstract

Liquid crystals playing a crucial role in material sciences show increasing potential applications in nanotechnology and industry. Generally, thermodynamic and dynamic properties of liquid crystals strongly depend on the corresponding force fields (FF); thus, it is necessary and urgent for us to establish a reliable force field for a given liquid crystal system. In this paper, we develop a new set of FF parameters for the 5CB (4-cyano-4'-pentylbiphenyl) molecule by reoptimizing some parameters of TraPPE-UA in order to reproduce the bulk density. This strategy for the construction of 5CB FF is rather advisable as it not only provides reliable values for the Lennard-Jones parameters but also reduces the computational cost and maintains FF transferability. Indeed, our simulation results show that the phase behavior, the order parameter, conformational features, neighboring molecular pair arrangements, and diffusion properties of 5CB can be reproduced very well. We further validate the transferability of this 5CB FF by extending it to the 8CB (4-cyano-4'-octylbiphenyl) system. As a result, both the nematic and the partial bilayer smectic phases (Sm-A(d)) and the nematic-isotropic and the smectic-nematic transition temperatures as well as the diffusion properties of 8CB are successfully reproduced. Therefore, this set of FF parameters originally designed for the 5CB molecule is reliable and transferable. Its effectiveness to model nCB series and molecules with similar chemical structures is expected.

Influence of electrostatic interactions on the properties of cyanobiphenyl liquid crystals predicted from atomistic molecular dynamics simulations

“…For the NP force field, the predicted densities are within less than 1% from experimental values, with the nematic phase deviation less than 0.5% and only a slight underestimation (still less than 1%) at higher temperatures. This agreement for the density is very encouraging, taking into account that many previous simulation works struggled to capture the density of 5CB bulk systems [23,33,66,67]. …”

“…Thanks to the constantly increasing performance and efficiency of computers, MD simulations of LC materials have become a great tool to investigate the link between molecular level details and macroscopic properties, including the phase behaviour. Different levels of modelling have been used for these investigations, ranging from a singlesite Gay-Berne model [14][15][16][17], many-site coarse-grained models [18][19][20][21][22], and united-atom models [23][24][25], all the way to fully atomistic models [26][27][28][29], as well as hybrid models [29][30][31][32][33][34][35]. Clearly, the reliability of any MD simulation strongly depends on the accuracy of the force field employed.…”

“…They also reported that if the standard assisted model building with energy refinement [38] force field was directly employed without optimisation, a 120 K overestimation of T NI was observed, and thus showed a poor transferability of the generic force field to 5CB. Recently, Zhang et al [23] conducted MD simulations of the 5CB systems using the TraPPE-UA [39] force field with carefully-tuned parameters of the LennardJones potentials. The resulting order parameter, density, dipole moment, molecular conformations, and diffusion anisotropy ratio were all found in excellent agreement with experiments.…”

Developing coarse-grained potentials for the prediction of multi-properties of trans-1,4-polybutadiene melt

“…15 Note that depending on whether to consider the torsion degrees of freedom on the coarse-grained level, the nonbonded parameters ε and σ in the CG force fields with the torsion interaction or not will be derived separately. Firstly we adjust ε and σ to reproduce the target density.…”

Order and Conformation of Biphenyl in Cyanobiphenyl Liquid Crystals: A Combined Atomistic Molecular Dynamics and 1H NMR Study

“…[1][2][3][4][5][6][7][8][9][10][11] Of course, the success of this effort is strictly connected to the quality of the force field (FF), the set of intra and intermolecular interactions employed, which must inevitably be tested, and/or the use of parameterised versus experimental observations. [1][2][3][4][5][6][7][8][9][10][11] Of course, the success of this effort is strictly connected to the quality of the force field (FF), the set of intra and intermolecular interactions employed, which must inevitably be tested, and/or the use of parameterised versus experimental observations.…”