论文标题
非平衡分子动力学和原子固体瞬时冷冻的连续建模
Non-equilibrium molecular dynamics and continuum modelling of transient freezing of atomistic solids
论文作者
论文摘要
在这项工作中，我们使用非平衡分子动力学模拟和连续传热理论研究了Lennard-Jones液体的短暂固化。模拟在平板形盒子中进行，其中放置在盒子中央的冷恒温器驱动液体的凝固。两个定义明确的固体前部从中心向外传播到盒子的末端，直到固化完成。配制了固体和液体密度之间差异的连续相变模型，以描述温度的演变以及凝固锋的位置。小型和大型纳米级系统的仿真结果，尺寸为$ 30.27 $ \，NM和$ 60.54 $ \，NM，与理论模型的预测进行了比较。在短暂的$ \ sim $ 20-40 PS和1-2.5 nm的固化前端的位移之后，我们发现模拟和连续性理论表现出良好的一致性。我们使用这个事实将模拟和理论方法结合起来，设计一个简单的程序来计算材料的潜热。我们还通过在超冷温度下淬灭液体，对均匀的冷冻过程进行模拟，即在没有温度梯度的情况下，在恒温下进行模拟。我们证明，同质冷冻的凝固速率比在同一恒温温度相同的相同尺寸的系统中获得的固体速度要快得多。我们的研究和结论应该对广泛的原子固体具有普遍的兴趣。
In this work we investigate the transient solidification of a Lennard-Jones liquid using non-equilibrium molecular dynamics simulations and continuum heat transfer theory. The simulations are performed in slab-shaped boxes, where a cold thermostat placed at the centre of the box drives the solidification of the liquid. Two well-defined solid fronts propagate outwards from the centre towards the ends of the box until solidification is completed. A continuum phase change model that accounts for the difference between the solid and the liquid densities is formulated to describe the evolution of the temperature and the position of the solidification front. Simulation results for a small and a large nanoscale system, of sizes $30.27$\,nm and $60.54$\,nm, are compared with the predictions of the theoretical model. Following a transient period of $\sim$20-40 ps and a displacement of the solidification front of 1-2.5 nm we find that the simulations and the continuum theory show good agreement. We use this fact to combine the simulation and theoretical approaches to design a simple procedure to calculate the latent heat of the material. We also perform simulations of the homogeneous freezing process, i.e. in the absence of a temperature gradient and at constant temperature, by quenching the liquid at supercooled temperatures. We demonstrate that the solidification rate of homogenous freezing is much faster than the one obtained under a thermal gradient for systems of the same size subject to the same thermostat temperature. Our study and conclusions should be of general interest to a wide range of atomistic solids.
