AI 中文总结
本文对比OrthoBoXY与Green-Kubo方法计算15种纯分子液体的剪切粘度，验证OrthoBoXY法的有限尺寸效应特性，改进其模拟块长度设置，可降低24倍计算成本且不损失精度。
AI 中文摘要
我们采用OrthoBoXY方法，通过平衡分子动力学（MD）模拟计算了15种纯分子液体的剪切粘度，并将其与通过Green-Kubo方法计算得到的粘度进行对比。两种方法得到的数据吻合度极高。本文展示了在计算OrthoBoXY数据时如何规避陷阱以获得最优结果。通过对多种系统尺寸的模拟，我们验证了分子液体的粘度在小至仅含250个分子的系统中，不受有限尺寸效应的影响。此外，我们还证明了粘度的标准误差也几乎与系统尺寸无关，这一现象源于两个因素的补偿效应：随系统尺寸增大，自扩散系数的精度不断提高，以及根据OrthoBoXY方程与系统尺寸相关的权重。基于此，我们建议，相比运行较大系统的较短模拟，采用较小系统并延长模拟时间更为可取。此外，我们还对近期提出的OrthoBoXY模拟块长度τ_block的“方案”进行了改进：对于高粘度系统，τ_block可安全地缩放1/8倍，大幅减少所需计算资源；对于低粘度系统，τ_block可安全地缩放1/4倍；对于高流动性系统，不应缩小τ_block以获得可靠结果。当使用仅含250个分子的较小系统时，这些改进措施可使计算成本较之前推荐的设置降低24倍，且不损失数值精度。
英文摘要
We calculated shear viscosities of 15 neat molecular liquids from equilibrium molecular dynamics (MD) simulations using the OrthoBoXY approach and compare them to viscosities calculated via the Green-Kubo method. Data from both methods agree very well. Here, we show how to avoid pitfalls while computing the OrthoBoXY-data to obtain optimal results. From simulations of multiple system sizes, we could verify that the viscosity of molecular liquids is not influenced by finite size effects down to systems as small as 250 molecules. Moreover, we demonstrate that also the standard error of the viscosity is nearly independent of the system size. This is shown to be a consequence of a compensation effect of an increasing accuracy of the self-diffusion coefficients with increasing systems-size and the system-size dependent weighting according to the OrthoBoXY-equation. As a consequence, we suggest that it is preferable to run simulations of smaller systems with longer simulation times rather than larger systems with shorter simulation runs. In addition, we discuss a refinement of the recently introduced "recipe" for OrthoBoXY simulations block-lengths $τ_\mathrm{block}$. Based on data from simulations with varying run-lengths, we suggest the following modification: for highly viscous systems, the value of $τ_\mathrm{block}$ might safely be scaled by a factor of $1/8$, significantly reducing the computational resources needed. For less viscous systems, the value of $τ_\mathrm{block}$ might safely be scaled by a factor of $1/4$. For systems with high fluidity, the value of $τ_\mathrm{block}$ should not be scaled down in order to achieve reliable results. When using a smaller system size of 250 molecules, these refinements are leading up to a 24-fold reduction in computational cost compared to the previous recommended set-up without sacrificing numerical accuracy.
Comments8 pages, 5 figures
