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arXiv 1008.1392cond-mat.softcond-mat.stat-mech
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可穿透球模型流体自扩散的分子动力学模拟研究

Molecular dynamics simulation study of self-diffusion for penetrable-sphere model fluids

Soong-Hyuck Suh, Chun-Ho Kim, Soon-Chul Kim, Andrés Santos

摘要:

采用分子动力学模拟模拟了具有有限能垒$ε$的可穿透球模型流体的扩散行为。自扩散系数由随时间变化的速度自相关函数和均方位移估算。详细的见解到团簇形成的可穿透的球体得到的Enskog因子,有效的粒子体积分数,平均自由程,和碰撞频率的软型可穿透和硬型反射碰撞。模拟数据进行比较,从玻尔兹曼动力学方程的理论预测和从一个简单的扩展到有限的$ε$的Enskog预测不可穿透的硬球($ε\to\infty$)。在$ε^*\equiv ε/k_BT=0.2$、$0.5$和$1.0$的情况下,理论和仿真结果之间存在合理的一致性。然而,对于致密的系统(包装分数$ϕ>0.6$)与一个高度排斥的能量障碍($ε^*=3.0$),观察到较差的协议,由于亚稳态静态效应的集群形成和动态效应的相关碰撞过程中,这些集群形成的颗粒。

英文摘要:

Molecular dynamics simulations are carried out to investigate the diffusion behavior of penetrable-sphere model fluids characterized by a finite energy barrier $ε$. The self-diffusion coefficient is evaluated from the time-dependent velocity autocorrelation function and mean-square displacement. Detailed insights into the cluster formation for penetrable spheres are gained from the Enskog factor, the effective particle volume fraction, the mean free path, and the collision frequency for both the soft-type penetrable and the hard-type reflective collisions. The simulation data are compared to theoretical predictions from the Boltzmann kinetic equation and from a simple extension to finite $ε$ of the Enskog prediction for impenetrable hard spheres ($ε\to\infty$). A reasonable agreement between theoretical and simulation results is found in the cases of $ε^*\equiv ε/k_BT=0.2$, $0.5$, and $1.0$. However, for dense systems (packing fraction $ϕ>0.6$) with a highly repulsive energy barrier ($ε^*=3.0$), a poorer agreement was observed due to metastable static effects of clustering formation and dynamic effects of correlated collision processes among these cluster-forming particles.

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