Department of Chemical Engineering, University College London, London WC1E 7JE, United Kingdom.
Department of Chemistry, Columbia University, New York, New York 10027, USA.
J Chem Phys. 2016 Dec 7;145(21):211925. doi: 10.1063/1.4966265.
Condensation of a liquid droplet from a supersaturated vapour phase is initiated by a prototypical nucleation event. As such it is challenging to compute its rate from atomistic molecular dynamics simulations. In fact at realistic supersaturation conditions condensation occurs on time scales that far exceed what can be reached with conventional molecular dynamics methods. Another known problem in this context is the distortion of the free energy profile associated to nucleation due to the small, finite size of typical simulation boxes. In this work the problem of time scale is addressed with a recently developed enhanced sampling method while contextually correcting for finite size effects. We demonstrate our approach by studying the condensation of argon, and showing that characteristic nucleation times of the order of magnitude of hours can be reliably calculated. Nucleation rates spanning a range of 10 orders of magnitude are computed at moderate supersaturation levels, thus bridging the gap between what standard molecular dynamics simulations can do and real physical systems.
从过饱和气相中凝结液滴是由典型的成核事件引发的。因此，从原子分子动力学模拟计算其速率是具有挑战性的。实际上，在实际的过饱和度条件下，凝结发生的时间尺度远远超过了传统分子动力学方法所能达到的时间尺度。在这种情况下，另一个已知的问题是由于典型模拟盒的小尺寸和有限尺寸，与成核相关的自由能分布的扭曲。在这项工作中，通过最近开发的增强采样方法解决了时间尺度问题，同时对有限尺寸效应进行了上下文校正。我们通过研究氩气的凝结来演示我们的方法，并表明可以可靠地计算出数量级为小时的特征成核时间。在中等过饱和度水平下计算了跨越 10 个数量级的成核速率，从而在标准分子动力学模拟所能达到的和实际物理系统之间架起了桥梁。
