Jeong Seongmin, Jho Yongseok, Zhou Xin
Asia-Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 790-784, South Korea.
Physics Department, POSTECH, Pohang, Gyeongbuk 790-784, South Korea.
Sci Rep. 2015 Nov 3;5:15955. doi: 10.1038/srep15955.
Although the microstructure of coexistence phase provides direct insights of the nucleation mechanism and their change is substantial in the phase transition, their study is limited due to the lack of suitable tools capturing the thermodynamically unstable transient states. We resolve this problem in computational study by introducing a generalized canonical ensemble simulation and investigate the morphological change of the nucleus during the water evaporation and condensation. We find that at very low pressure, where the transition is first order, classical nucleation theory holds approximately. A main nucleus is formed in the supersaturation near spinodal, and the overall shape of the nucleus is finite and compact. On increasing the pressure of the system, more nuclei are formed even before spinodal. They merge into a larger nuclei with a smaller free energy penalty to form ramified shapes. We suggest order parameters to describe the extent of fluctuation, and their relation to the free energy profile.
尽管共存相的微观结构为成核机制提供了直接的见解，并且它们在相变过程中的变化很大，但由于缺乏捕获热力学不稳定瞬态的合适工具，对它们的研究受到限制。我们通过引入广义正则系综模拟在计算研究中解决了这个问题，并研究了水蒸发和凝结过程中核的形态变化。我们发现，在非常低的压力下，转变是一级的，经典成核理论大致成立。在亚稳极限附近的过饱和状态下形成一个主要的核，并且核的整体形状是有限且紧凑的。随着系统压力的增加，甚至在亚稳极限之前就会形成更多的核。它们合并成一个具有较小自由能损失的更大的核，形成分支状形状。我们提出了序参量来描述涨落程度及其与自由能分布的关系。
