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Segregation and ordering at alloys surfaces: modelling and experiment confronted

机译：合金表面的偏析和有序化：面临的建模和实验

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Model calculations combining the Monte Carlo (MC) method and a suitable energy model are proposed as fully complementary to experiments in order to gain insight in segregation and other surface phenomena, deployed by materials in order to minimise their surface free energy and hence their total Gibbs free energy. In the confrontation between experiments and modelling. it is basically assumed that the surface, as observed in the experiments, corresponds to the equilibrium situation of minimal Gibbs free energy. The entropy part is modelled by the stochastic nature of Monte Carlo simulations, while the energy part is taken into account by the (modified) embedded atom method ((M)EAM). Special attention is paid to the derivation of model parameters that are specific for the alloy under study. For it appears that in several cases the experimental data can only correctly be reproduced with these specific EAM parameters. This article further focuses on the determination of the degree of order in the bulk. Simulations according to the Grand Canonical Ensemble require the difference in chemical potential between the components. A novel approach is presented for deriving this parameter both for slightly off-stoichiometric ordered alloys and for disordered alloys. Results of MC/(M)EAM simulations are presented for the surfaces of five catalytically important binary alloys: Au75Pd25(1 10), Cu75Pd25(1 1 0), Pt50Ni50(l 0 0), 0 10) and (I 1 1), Pt80Fe20(l 1 1) and Pt75Sn25(l 1 1). It can be concluded that these simulations yield excellent predictions for surface modifications and are a very powerful tool to model and understand surfaces at equilibrium. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 63]
机译：提出了将蒙特卡洛（MC）方法和合适的能量模型相结合的模型计算，作为对实验的完全补充，目的是获得偏析和其他表面现象的见解，并通过材料展开以最小化其表面自由能，从而使它们的总Gibbs最小化自由能。在实验和建模之间的对抗中。基本上假定，如在实验中观察到的，表面对应于最小吉布斯自由能的平衡状态。熵部分是通过蒙特卡洛模拟的随机性质建模的，而能量部分是通过（修改的）嵌入原子方法（（M）EAM）考虑的。要特别注意要研究的合金特有的模型参数的推导。在某些情况下，似乎只能使用这些特定的EAM参数正确地复制实验数据。本文进一步着重于确定整体中的有序度。根据大正则合奏进行的模拟要求组件之间的化学势不同。提出了一种新颖的方法来为化学计量稍有序的合金和无序合金导出此参数。给出了五种具有催化作用的重要二元合金表面的MC /（M）EAM模拟结果：Au75Pd25（1 10），Cu75Pd25（1 1 0），Pt50Ni50（l 0 0），0 10）和（I 1 1） ，Pt80Fe20（l 1 1）和Pt75Sn25（l 1 1）。可以得出结论，这些模拟对表面改性产生了出色的预测，并且是在平衡状态下建模和理解表面的强大工具。 （C）2003 Elsevier Science B.V.保留所有权利。 [参考：63]

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