GPU-Accelerated Molecular Dynamics Simulation to Study Liquid Crystal Phase Transition Using Coarse-Grained Gay-Berne Anisotropic Potential

Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers. For identical mesogens in three different molecules, on cooling from fully isotropic melts, the small molecules form a single-domain smectic-B phase, while the main-chain LC polymers prefer a single-domain nematic phase as a result of connective restraints in neighboring mesogens. The phase transition of side-chain LC polymers undergoes a two-step process: nucleation of nematic islands and formation of multi-domain nematic texture. The particular behavior originates in the fact that the rotational orientation of the mesogenes is hindered by the polymer backbones. Both the global distribution and the local orientation of mesogens are critical for the phase transition of anisotropic particles. Furthermore, compared with the MD simulation in LAMMPS, our GPU-accelerated code is about 4 times faster than the GPU version of LAMMPS and at least 200 times faster than the CPU version of LAMMPS. This study clearly shows that GPU-accelerated MD simulation with GB potential in GALAMOST can efficiently handle systems with anisotropic particles and interactions, and accurately explore phase differences originated from molecular structures.

Gay-Berne（GB）势能被视为各向异性粒子模拟，特别是液晶（LC）介晶模拟的精准模型。但其计算复杂度较高，导致大型体系的模拟过程耗时极久。本文中，我们开发了一种在GALAMOST软件包中实现粗粒化GB势能的GPU加速分子动力学（MD）模拟方法，用于探究小分子、主链型或侧链型聚合物中介晶的液晶相变行为。针对三种不同分子结构中的相同介晶，从完全各向同性熔体冷却时，小分子会形成单畴近晶B相；而主链型液晶聚合物因相邻介晶间的连接约束，更易形成单畴向列相。侧链型液晶聚合物的相变则遵循两步过程：向列岛成核与多畴向列织构的形成。该特殊行为源于聚合物主链对介晶旋转取向的阻碍作用。介晶的整体分布与局部取向均对各向异性粒子的相变过程至关重要。此外，相较于LAMMPS中的MD模拟，我们的GPU加速代码的运行速度约为LAMMPS GPU版本的4倍，且至少比LAMMPS CPU版本快200倍。本研究明确表明，在GALAMOST中实现的搭载粗粒化GB势能的GPU加速MD模拟，可高效处理含各向异性粒子与相互作用的体系，并准确揭示源自分子结构差异的相变行为差异。