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Adsorption of cobalt on graphene: Electron correlation effects from a quantum chemical perspective

机译：石墨烯上钴的吸附：从量子化学角度看电子相关效应

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In this work, we investigate the adsorption of a single cobalt atom (Co) on graphene by means of the complete active space self-consistent field approach, additionally corrected by the second-order perturbation theory. The local structure of graphene is modeled by a planar hydrocarbon cluster (C24H12). Systematic treatment of the electron correlations and the possibility to study excited states allow us to reproduce the potential energy curves for different electronic configurations of Co. We find that upon approaching the surface, the ground-state configuration of Co undergoes several transitions, giving rise to two stable states. The first corresponds to the physisorption of the adatom in the high-spin 3d~74s~2 (S = 3/2) configuration, while the second results from the chemical bonding formed by strong orbital hybridization, leading to the low-spin 3d~9 (S = 1/2) state. Due to the instability of the 3d~9 configuration, the adsorption energy of Co is small in both cases and does not exceed 0.35 e V. We analyze the obtained results in terms of a simple model Hamiltonian that involves Coulomb repulsion (U) and exchange coupling (J) parameters for the 3d shell of Co, which we estimate from first-principles calculations. We show that while the exchange interaction remains constant upon adsorption (~1.1 eV), the Coulomb repulsion significantly reduces for decreasing distances (from 5.3 to 2.6 ± 0.2 eV). The screening of U favors higher occupations of the 3d shell and thus is largely responsible for the interconfigurational transitions of Co. Finally, we discuss the limitations of the approaches that are based on density functional theory with respect to transition metal atoms on graphene, and we conclude that a proper account of the electron correlations is crucial for the description of adsorption in such systems.
机译：在这项工作中，我们通过完整的有源空间自洽场方法研究了单个钴原子（Co）在石墨烯上的吸附，并通过二阶微扰理论对其进行了修正。石墨烯的局部结构由平面烃簇（C24H12）建模。电子相关性的系统处理和研究激发态的可能性使我们能够再现Co的不同电子构型的势能曲线。我们发现，在接近表面时，Co的基态构型经历了几次跃迁，从而产生了两个稳定状态。第一个对应于高自旋3d〜74s〜2（S = 3/2）构型中吸附原子的物理吸附，而第二个对应于强轨道杂交形成的化学键合，从而导致了低自旋3d〜 9（S = 1/2）状态。由于3d〜9构型的不稳定性，在两种情况下，Co的吸附能均很小，且不超过0.35 eV。我们采用涉及库仑排斥（U）和交换的简单哈密顿模型对所得结果进行分析。 Co的3d壳的耦合（J）参数，我们从第一性原理计算中估算出来。我们显示，虽然交换相互作用在吸附后保持恒定（〜1.1 eV），但库仑排斥力随着距离的减小而显着降低（从5.3到2.6±0.2 eV）。 U的筛选有利于3d壳的更高占据，因此在很大程度上负责Co的构型转变。最后，我们讨论了基于密度泛函理论的方法对石墨烯上过渡金属原子的局限性，并且得出的结论是，正确描述电子相关性对于描述此类系统中的吸附至关重要。

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  • 来源
    《Physical review》 |2012年第7期|p.075422.1-075422.11|共11页
  • 作者

    A. N. Rudenko; F. J. Keil; M. I. Katsnelson; A. I. Lichtenstein;

  • 作者单位

    Institute of Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Strasse 38, D-21073 Hamburg, Germany;

    Institute of Chemical Reaction Engineering, Hamburg University of Technology, Eissendorfer Strasse 38, D-21073 Hamburg, Germany;

    Institute for Molecules and Materials, Radboud University Nijmegen, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands;

    Institute of Theoretical Physics, University of Hamburg, Jungiusstrasse 9, D-20355 Hamburg, Germany;

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