Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
J Phys Condens Matter. 2012 Jun 6;24(22):225404. doi: 10.1088/0953-8984/24/22/225404. Epub 2012 May 15.
We develop two new modified embedded-atom method (MEAM) potentials for elemental iron, intended to reproduce the experimental phase stability with respect to both temperature and pressure. These simple interatomic potentials are fitted to a wide variety of material properties of bcc iron in close agreement with experiments. Numerous defect properties of bcc iron and bulk properties of the two close-packed structures calculated with these models are in reasonable agreement with the available first-principles calculations and experiments. Performance at finite temperatures of these models has also been examined using Monte Carlo simulations. We attempt to reproduce the experimental iron polymorphism at finite temperature by means of free energy computations, similar to the procedure previously pursued by Müller et al (2007 J. Phys.: Condens. Matter 19 326220), and re-examine the adequacy of the conclusion drawn in the study by addressing two critical aspects missing in their analysis: (i) the stability of the hcp structure relative to the bcc and fcc structures and (ii) the compatibility between the temperature and pressure dependences of the phase stability. Using two MEAM potentials, we are able to represent all of the observed structural phase transitions in iron. We discuss that the correct reproductions of the phase stability among three crystal structures of iron with respect to both temperature and pressure are incompatible with each other due to the lack of magnetic effects in this class of empirical interatomic potential models. The MEAM potentials developed in this study correctly predict, in the bcc structure, the self-interstitial in the (110) orientation to be the most stable configuration, and the screw dislocation to have a non-degenerate core structure, in contrast to many embedded-atom method potentials for bcc iron in the literature.
我们为元素铁开发了两种新的改进嵌入原子法 (MEAM) 势，旨在根据温度和压力重现实验相稳定性。这些简单的原子间势与实验密切吻合，可拟合 bcc 铁的各种材料特性。使用这些模型计算的 bcc 铁的大量缺陷性质和体相性质与可用的第一性原理计算和实验结果吻合良好。还使用蒙特卡罗模拟检查了这些模型在有限温度下的性能。我们试图通过自由能计算来重现有限温度下的实验铁多晶型性，类似于 Müller 等人（2007 J. Phys.：Condens. Matter 19 326220）以前采用的方法，并通过解决他们分析中缺少的两个关键方面来重新检查该研究结论的充分性：（i）hcp 结构相对于 bcc 和 fcc 结构的稳定性，以及（ii）相稳定性的温度和压力依赖性之间的兼容性。使用两种 MEAM 势，我们能够表示铁中所有观察到的结构相变。我们讨论了由于缺乏这种经验原子间势模型类中的磁效应，铁的三种晶体结构在温度和压力方面的正确相稳定性再现彼此之间是不兼容的。本研究中开发的 MEAM 势正确预测，在 bcc 结构中，（110）取向的自间隙是最稳定的构型，而螺位错具有非简并的核心结构，与文献中许多 bcc 铁的嵌入原子法势相反。
