Classical nucleation theory describes the formation of the first solids from supercooled liquids and predicts an average waiting time for a system to freeze as it is cooled below the melting temperature. For systems at low to moderate undercooling, waiting times are too long for freezing to be observed via simulation. Here a system can be described by estimated thermodynamic properties, or by extrapolation from practical conditions where thermodynamic properties can be fit directly to simulations. In the case of crystallizing Earth's solid iron inner core, these thermodynamic parameters are not well known and waiting times from simulations must be extrapolated over approximately 60 orders of magnitude. In this work, we develop a new approach negating the need for freezing to be observed. We collect statistics on solidlike particles in molecular dynamic simulations of supercooled liquids at 320 GPa. This allows estimation of waiting times at temperatures closer to the melting point than is accessible to other techniques and without prior thermodynamic insight or assumption. Our method describes the behavior of nucleation at otherwise inaccessible conditions such that the nucleation of any system at small undercooling can be characterized alongside the thermodynamic quantities which define the first formed solids.

中文翻译：

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使用过冷液体的分子动力学模拟探测地核中铁的成核

经典成核理论描述了从过冷液体中形成第一个固体，并预测了系统在低于熔化温度时冷却到冻结的平均等待时间。对于处于低到中度过冷度的系统，等待时间太长而无法通过模拟观察到冻结。在这里，一个系统可以通过估计的热力学特性来描述，或者通过从实际条件外推来描述，其中热力学特性可以直接适合模拟。在结晶地球的固体铁内核的情况下，这些热力学参数并不为人所知，模拟的等待时间必须外推大约 60 个数量级。在这项工作中，我们开发了一种新方法，无需观察冻结。我们在 320 GPa 的过冷液体的分子动力学模拟中收集了类固体粒子的统计数据。这允许估计在接近熔点的温度下的等待时间，而不是其他技术可以访问的，并且无需事先了解热力学或假设。我们的方法描述了在其他条件下无法达到的成核行为，因此任何系统在小过冷下的成核都可以与定义第一个形成的固体的热力学量一起表征。