Abstract First principles DFT calculations are used to gain insights into the molecular mechanism of Cr passivation of FeCr alloy surfaces. The systems studied represent early stages of oxidation of FeCr alloys when the oxide layers extend just a few atomic layers into the bulk. A Monte-Carlo atom-swapping algorithm was developed to efficiently explore possible atomic positions and identify the most promising structures that yield overall energy lowering. Analysis of the resulting low energy structures show that the surface oxide layer is rich in chromium while there is a reduction in chromium in the metallic phase near the alloy-oxide interface. Furthermore, there is an increased concentration of Fe near the oxide-air surface. Analysis of the molecular structure of the oxide layers found that oxidized Cr was predominantly in the Cr2O3 phase, while oxidized Fe was present as both FeO and Fe2O3. We propose that the oxidative variability of Fe facilitates O diffusion in the iron-rich phases because of the range of geometries available for accommodating the O atom. In contrast, O diffusion is less facile in Cr, which has little variability in oxidation state.

中文翻译：

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对不锈钢表面铬钝化的分子机制的计算洞察

摘要 第一性原理 DFT 计算用于深入了解 FeCr 合金表面 Cr 钝化的分子机制。所研究的系统代表了 FeCr 合金氧化的早期阶段，当氧化层仅延伸到几个原子层时。开发了蒙特卡罗原子交换算法，以有效地探索可能的原子位置并确定最有希望的结构，从而降低整体能量。对所得低能量结构的分析表明，表面氧化层富含铬，而合金-氧化物界面附近的金属相中的铬减少。此外，氧化物-空气表面附近的 Fe 浓度增加。分析氧化物层的分子结构发现氧化的 Cr 主要在 Cr2O3 相中，而氧化的 Fe 以 FeO 和 Fe2O3 的形式存在。我们提出，由于可用于容纳 O 原子的几何形状范围，Fe 的氧化变异性促进了 O 在富铁相中的扩散。相比之下，O 在 Cr 中的扩散不太容易，Cr 的氧化态变化很小。