Abstract
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.
Highlights
Liquid crystals (LC) can be assembled from either small molecules [1, 2] or polymers [3,4,5,6]
We developed graphics processing units (GPU)-accelerated molecular dynamics (MD) simulations equipped with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions
The success of GPU acceleration may benefit from two important aspects: (1) the computational power of a single GPU, such as Tesla K20C with a theoretical peak 3.95 Teraflops of single precision computation throughput, is usually more than a hundred times faster than that of a CPU core, such as Xeon E5-2687w with 21.56 Gigaflops per core; (2) GALAMOST is highly optimized such as the memory sorting technique which can significantly reduce the time for nonbonded force calculation, and the elimination of inter-memory communication[57]
Summary
Liquid crystals (LC) can be assembled from either small molecules [1, 2] or polymers [3,4,5,6]. A combination of coarse-grained Gay-Berne (GB) model [16,17,18] and graphics processing units (GPU)-accelerated algorithms [19,20,21,22] should be a highly promising way to provide simulation accuracy and efficiency in the study of larger systems considering more details of anisotropic particles, especially for LC phase transitions. Compared with well studied MCLCP, for SCLCP, the structure of polymer backbone, the grafting density, the pendant mesogens, and the flexible spacer length all exert important influence on the mesophase morphology [43]. We developed GPU-accelerated MD simulations equipped with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions.
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