Espinosa J R, Vega C, Sanz E
Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
J Chem Phys. 2014 Oct 7;141(13):134709. doi: 10.1063/1.4896621.
The interfacial free energy between a crystal and a fluid, γcf, is a highly relevant parameter in phenomena such as wetting or crystal nucleation and growth. Due to the difficulty of measuring γcf experimentally, computer simulations are often used to study the crystal-fluid interface. Here, we present a novel simulation methodology for the calculation of γcf. The methodology consists in using a mold composed of potential energy wells to induce the formation of a crystal slab in the fluid at coexistence conditions. This induction is done along a reversible pathway along which the free energy difference between the initial and the final states is obtained by means of thermodynamic integration. The structure of the mold is given by that of the crystal lattice planes, which allows to easily obtain the free energy for different crystal orientations. The method is validated by calculating γcf for previously studied systems, namely, the hard spheres and the Lennard-Jones systems. Our results for the latter show that the method is accurate enough to deal with the anisotropy of γcf with respect to the crystal orientation. We also calculate γcf for a recently proposed continuous version of the hard sphere potential and obtain the same γcf as for the pure hard sphere system. The method can be implemented both in Monte Carlo and Molecular Dynamics. In fact, we show that it can be easily used in combination with the popular Molecular Dynamics package GROMACS.
晶体与流体之间的界面自由能γcf，是诸如润湿、晶体成核与生长等现象中一个高度相关的参数。由于通过实验测量γcf存在困难，计算机模拟常被用于研究晶体 - 流体界面。在此，我们提出一种计算γcf的新型模拟方法。该方法在于使用由势能阱组成的模具，在共存条件下诱导流体中形成晶体平板。这种诱导沿着一条可逆路径进行，通过热力学积分可得到初始态与终态之间的自由能差。模具的结构由晶格平面的结构给出，这使得能够轻松获得不同晶体取向的自由能。通过为先前研究的系统（即硬球系统和 Lennard - Jones 系统）计算γcf来验证该方法。我们对后者的结果表明，该方法足够精确，能够处理γcf相对于晶体取向的各向异性。我们还为最近提出的硬球势的连续版本计算了γcf，并得到了与纯硬球系统相同的γcf。该方法可在蒙特卡罗方法和分子动力学方法中实现。实际上，我们表明它可以很容易地与流行的分子动力学软件包 GROMACS 结合使用。
