We present a systematic study of the self-diffusion coefficient for a fluid of particles interacting via the square-well pair potential by means of molecular dynamics simulations in the canonical (N, V, T) ensemble. The discrete nature of the interaction potential is modeled by the constant force approximation, and the self-diffusion coefficient is determined for several fluid densities at supercritical thermodynamic states. The dependence of the self-diffusion coefficient on the potential range λ is analyzed in the range of 1.1 ≤ λ ≤ 1.5. The obtained simulation results are in agreement with the self-diffusion coefficient predicted by the Enskog method. Additionally, we show that the diffusion coefficient is very sensitive to the potential range λ. Our results for the self-diffusion coefficient times density extrapolate well to the values in the zero-density limit obtained from the Chapman-Enskog theory for dilute gases. The constant force approximation used in this work to model the discrete pair potentials has shown to be an excellent scheme to compute the transport properties of square-well fluids using molecular dynamics simulations. Finally, the simulation results presented here are useful for improving theoretical approaches, such as the Enskog method.

中文翻译：

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恒力方法中分子动力学模拟对方井流体的自扩散系数

我们通过规范（N，V，T）系中的分子动力学模拟，对通过方阱对势相互作用的粒子流体的自扩散系数进行了系统的研究。相互作用势的离散性质通过恒力逼近进行建模，并确定了在超临界热力学状态下几种流体密度的自扩散系数。上的电势范围内的自扩散系数的依赖性λ分析中的1.1的范围≤ λ≤1.5。仿真结果与Enskog方法预测的自扩散系数吻合。此外，我们表明扩散系数对电势范围λ非常敏感。我们的自扩散系数乘以密度的结果很好地外推到从Chapman-Enskog理论获得的稀气体的零密度极限值中。在这项工作中用于模拟离散对电位的恒力逼近已证明是一种使用分子动力学模拟来计算方井流体的输运特性的出色方案。最后，此处提供的仿真结果对于改进理论方法（例如Enskog方法）很有用。