All-atom molecular dynamics simulations were performed on 4-heptyl-4'-cyanobiphenyl (7CB) to study the mechanism of heat conduction in this nematic liquid crystal atomistically. To describe 7CB properly, the AMBER-type force field was optimized for the dihedral parameter of biphenyl and the Lennard-Jones parameters. The molecular dynamics calculation using the optimized force field well reproduced the experimental values of the isotropic-nematic phase transition temperature, density, and anisotropy of the thermal conductivity. Furthermore, the contributions of convection, intramolecular interaction, and intermolecular interaction to the thermal conductivity were determined by performing thermal conductivity decomposition analysis. According to the analysis, the contributions of convection, bond stretching, and bond bending interactions were higher in the direction parallel to the nematic director than that perpendicular to the director, which is the origin of the anisotropy in the nematic phase. This result indicates that the anisotropy is caused by well-aligned covalent bonds and high mobility parallel to the director. This quantitative description of the mechanism of heat conduction of 7CB is foreseen to provide new insights toward designing highly thermally conductive liquid-crystalline materials.

中文翻译：

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液晶4-庚基-4'-氰基联苯中各向异性导热的原子机理：全原子分子动力学。

在4-庚基-4'-氰基联苯（7CB）上进行了全原子分子动力学模拟，以原子方式研究了该向列液晶的热传导机理。为了正确描述7CB，针对联苯的二面参数和Lennard-Jones参数优化了AMBER型力场。使用优化的力场进行的分子动力学计算很好地再现了各向同性-向列相变温度，密度和导热系数各向异性的实验值。此外，通过进行热导率分解分析来确定对流，分子内相互作用和分子间相互作用对热导率的贡献。根据分析，对流，粘结拉伸，在平行于向列导向器的方向上，键弯曲相互作用要比垂直于指向矢的方向高，这是向列相中各向异性的起源。该结果表明各向异性是由于共价键排列正确和平行于指向矢的高迁移率引起的。可以预见的是，这种7CB导热机理的定量描述将为设计高导热液晶材料提供新的见解。