NVT系综中成核的种子方法：过拉伸Lennard Jones流体中气泡空化的情况
Seeding Approach to nucleation in the NVT ensemble: the case of bubble cavitation in overstretched Lennard Jones fluids
摘要：
模拟被广泛用于研究一阶相变中的成核，这是由于它们可以获得相关的长度和时间尺度。然而，模拟面临的问题，成核是一个激活的过程。因此，需要稀有事件模拟技术来促进临界核的形成。播种方法，其中的模拟开始与核已经形成，已被证明是非常有用的，有效地提供估计的成核率的一个广泛的数量级。到目前为止，播种已经在NPT系综中使用，其中核生长或重新溶解。因此，必须运行几个轨道，以找到使种子核临界的热力学条件。此外，原子核的寿命很短，因此获得其性质的统计数据很差。为了解决这些缺点，我们将种子方法扩展到NVT系综。研究了可稳态Lennard Jones流体中气泡的成核问题。我们表明，在NVT合奏，这是可能的平衡和稳定的临界气泡很长一段时间。从NVT-引晶中推断的成核速率与从NPT-引晶中推断的成核速率完全一致。前者非常适合获得沿等温线的成核速率，而后者在需要恒压下成核速率与温度的关系时更可取。使用NVT-Seeding时，应注意有限尺寸效应。需要进一步的工作将NVT播种扩展到其他种类的相变。
英文摘要：
Simulations are widely used to study nucleation in first order phase transitions due to the fact that they have access to the relevant length and time scales. However, simulations face the problem that nucleation is an activated process. Therefore, rare event simulation techniques are needed to promote the formation of the critical nucleus. The Seeding method, where the simulations are started with the nucleus already formed, has proven quite useful in efficiently providing estimates of the nucleation rate for a wide range of orders of magnitude. So far, Seeding has been employed in the NPT ensemble, where the nucleus either grows or redissolves. Thus, several trajectories have to be run in order to find the thermodynamic conditions that make the seeded nucleus critical. Moreover, the nucleus lifetime is short and the statistics for obtaining its properties is consequently poor. To deal with these shortcomings we extend the Seeding method to the NVT ensemble. We focus on the problem of bubble nucleation in a mestastable Lennard Jones fluid. We show that, in the NVT ensemble, it is possible to equilibrate and stabilise critical bubbles for a long time. The nucleation rate inferred from NVT-Seeding is fully consistent with that coming from NPT-Seeding. The former is quite suitable to obtain the nucleation rate along isotherms, whereas the latter is preferable if the dependence of the rate with temperature at constant pressure is required. Care should be taken with finite size effects when using NVT-Seeding. Further work is required to extend NVT seeding to other sorts of phase transitions.
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