Perego C, Salvalaglio M, Parrinello M
Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
Institute of Computational Science, Università della Svizzera Italiana, Lugano, Switzerland.
J Chem Phys. 2015 Apr 14;142(14):144113. doi: 10.1063/1.4917200.
Molecular dynamics studies of chemical processes in solution are of great value in a wide spectrum of applications, which range from nano-technology to pharmaceutical chemistry. However, these calculations are affected by severe finite-size effects, such as the solution being depleted as the chemical process proceeds, which influence the outcome of the simulations. To overcome these limitations, one must allow the system to exchange molecules with a macroscopic reservoir, thus sampling a grand-canonical ensemble. Despite the fact that different remedies have been proposed, this still represents a key challenge in molecular simulations. In the present work, we propose the Constant Chemical Potential Molecular Dynamics (CμMD) method, which introduces an external force that controls the environment of the chemical process of interest. This external force, drawing molecules from a finite reservoir, maintains the chemical potential constant in the region where the process takes place. We have applied the CμMD method to the paradigmatic case of urea crystallization in aqueous solution. As a result, we have been able to study crystal growth dynamics under constant supersaturation conditions and to extract growth rates and free-energy barriers.
溶液中化学过程的分子动力学研究在从纳米技术到药物化学等广泛的应用领域中具有重要价值。然而,这些计算受到严重的有限尺寸效应的影响,例如随着化学过程的进行溶液逐渐耗尽,这会影响模拟结果。为了克服这些限制,必须允许系统与宏观储库交换分子,从而对巨正则系综进行采样。尽管已经提出了不同的补救方法,但这仍然是分子模拟中的一个关键挑战。在本工作中,我们提出了恒化学势分子动力学(CμMD)方法,该方法引入了一个外力来控制感兴趣的化学过程的环境。这个外力从有限的储库中抽取分子,在过程发生的区域保持化学势恒定。我们已将CμMD方法应用于水溶液中尿素结晶的典型案例。结果,我们能够研究在恒定过饱和条件下的晶体生长动力学,并提取生长速率和自由能垒。