Neimark Alexander V, Vishnyakov Aleksey
Center for Modeling and Characterization of Nanoporous Materials, TRI/Princeton, Princeton, New Jersey 08542, USA.
J Chem Phys. 2005 May 1;122(17):174508. doi: 10.1063/1.1888389.
A new rigorous Monte Carlo simulation approach is employed to study nucleation barriers for droplets in Lennard-Jones fluid. Using the gauge cell method we generate the excess isotherm of critical clusters in the size range from two to six molecular diameters. The ghost field method is employed to compute the cluster free energy and the nucleation barrier with desired precision of (1-2)kT. Based on quantitative results obtained by Monte Carlo simulations, we access the limits of applicability of the capillarity approximation of the classical nucleation theory and the Tolman equation. We show that the capillarity approximation corrected for vapor nonideality and liquid compressibility provides a reasonable assessment for the size of critical clusters in Lennard-Jones fluid; however, its accuracy is not sufficient to predict the nucleation barriers for making practical estimates of the rate of nucleation. The established dependence of the droplet surface tension on the droplet size cannot be approximated by the Tolman equation for small droplets of radius less than four molecular diameters. We confirm the conclusion of ten Wolde and Frenkel [J. Chem. Phys. 109, 9901 (1998)] that integration of the normal component of the Irving-Kirkwood pressure tensor severely underestimates the nucleation barriers for small clusters.
采用一种新的严格蒙特卡罗模拟方法来研究 Lennard-Jones 流体中液滴的成核势垒。使用规范单元法，我们生成了尺寸范围从两个到六个分子直径的临界团簇的过量等温线。采用虚场法以 (1 - 2)kT 的所需精度计算团簇自由能和成核势垒。基于蒙特卡罗模拟获得的定量结果，我们探讨了经典成核理论的毛细近似和托尔曼方程的适用范围。我们表明，针对蒸汽非理想性和液体可压缩性修正后的毛细近似为 Lennard-Jones 流体中临界团簇尺寸提供了合理评估；然而，其精度不足以预测成核势垒以实际估计成核速率。对于半径小于四个分子直径的小液滴，液滴表面张力对液滴尺寸的既定依赖性不能用托尔曼方程近似。我们证实了 ten Wolde 和 Frenkel [《化学物理杂志》109, 9901 (1998)] 的结论，即欧文 - 柯克伍德压力张量法向分量的积分严重低估了小团簇的成核势垒。
