Cu/Ag EAM potential optimized for heteroepitaxial diffusion from ab initio data
Cu/Ag EAM potential optimized for heteroepitaxial diffusion from ab initio data
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DOI：
10.1088/0965-0393/17/5/055012
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发表时间：
2009-01
影响因子：
3.3
通讯作者：
Henry H. Wu;D. Trinkle
中科院分区：
文献类型：
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作者：
Henry H. Wu;D. Trinkle
摘要：通过拟合从头算数据，对Ag(1 1 1)上的Cu优化了一种二元嵌入原子法（EAM）势。拟合数据库由Ag(1 1 1)上Cu单体和二聚体的密度泛函理论（DFT）计算组成，特别是它们的相对能量、吸附原子高度和二聚体间距。我们从米申（Mishin）的Cu - Ag EAM势出发，首先修改Cu - Ag对势以匹配面心立方（FCC）/密排六方（HCP）位点能差，然后对整个数据库进行Cu - Cu对势优化。这种优化方法产生的势与之前的EAM以及一种表面嵌入原子法（SEAM）优化势相比，在Cu单体、二聚体和三聚体的DFT计算中具有更好的一致性。在三聚体计算中，优化后的势得出了FCC和HCP三聚体之间的DFT相对能量，尽管预测的基态不同。我们使用优化后的势来计算Cu单体、二聚体和三聚体的扩散势垒。预测的单体势垒与DFT相同，而单体和二聚体的实验势垒比此处预测的要低。我们将与实验的差异归因于DFT对表面吸附能的高估，并提出了一种简单的修正方法。我们的结果表明，这种优化方法适用于其他异质外延系统；并且优化后的Cu - Ag EAM可应用于Ag(1 1 1)上更大Cu岛的研究。
Abstract A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(1 1 1) by fitting to ab initio data. The fitting database consists of DFT calculations of Cu monomers and dimers on Ag(1 1 1), specifically their relative energies, adatom heights, and dimer separations. We start from the Mishin Cu–Ag EAM potential and first modify the Cu–Ag pair potential to match the FCC/HCP site energy difference then include Cu–Cu pair potential optimization for the entire database. The potential generated from this optimization method gives better agreement to DFT calculations of Cu monomers, dimers, and trimers than previous EAMs as well as a SEAM optimized potential. In trimer calculations, the optimized potential produces the DFT relative energy between FCC and HCP trimers, though a different ground state is predicted. We use the optimized potential to calculate diffusion barriers for Cu monomers, dimers, and trimers. The predicted monomer barrier is the same as DFT, while experimental barriers for monomers and dimers are lower than predicted here. We attribute the difference with experiment to the overestimation of surface adsorption energies by DFT and a simple correction is presented. Our results show that this optimization method is suitable for other heteroepitaxial systems; and that the optimized Cu–Ag EAM can be applied in the study of larger Cu islands on Ag(1 1 1).