Lazar Petr, Granatier Jaroslav, Klimeš Jiří, Hobza Pavel, Otyepka Michal
Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, tr. 17. listopadu 12, 771 46 Olomouc, Czech Republic.
Phys Chem Chem Phys. 2014 Oct 14;16(38):20818-27. doi: 10.1039/c4cp02608j. Epub 2014 Aug 28.
Recent theoretical simulations predicted that graphene decorated with Ir adatoms could realize a two-dimensional topological insulator with a substantial band gap. Our understanding of how the electronic properties of graphene change in the presence of metal adatoms is however still limited, as the binding is quite complex involving static and dynamic correlation effects together with relativistic contributions, which makes the theoretical description of such systems quite challenging. We applied the quantum chemical complete active space second order perturbation theory (CASPT2) method and density functional theory beyond the standard local density functional approach including relativistic spin-orbit coupling (SOC) effects on Ir-benzene and Ir-graphene complexes. The CASPT2-SOC method revealed a strong binding affinity of Ir for benzene (33.1 kcal mol(-1)) at a 1.81 Å distance, which was of a single reference character, and a weaker binding affinity (6.3 kcal mol(-1)) at 3.00 Å of a multireference character. In the Ir-graphene complex, the quartet ground-state of the Ir atom changed to the doublet state upon adsorption, and the binding energy predicted by optB86b-vdW-SOC functional remained high (33.8 kcal mol(-1)). In all cases the dynamic correlation effects significantly contributed to the binding. The density of states calculated with the hybrid functional HSE06 showed that the gap of 0.3 eV was induced in graphene by the adsorbed Ir atom even in scalar relativistic calculation, in contrast to metallic behaviour predicted by local density approximation. The results suggest that the strong correlation effects contribute to the opening of the band gap in graphene covered with the Ir adatoms. The value of the magnetic anisotropy energy of 0.1 kcal mol(-1) predicted by HSE06 is lower than those calculated using local functionals.
最近的理论模拟预测，用铱原子修饰的石墨烯可以实现具有可观带隙的二维拓扑绝缘体。然而，我们对石墨烯在金属原子存在下电子性质如何变化的理解仍然有限，因为这种结合相当复杂，涉及静态和动态相关效应以及相对论贡献，这使得对此类系统的理论描述颇具挑战性。我们应用了量子化学完全活性空间二阶微扰理论（CASPT2）方法以及超越标准局域密度泛函方法的密度泛函理论，包括对铱 - 苯和铱 - 石墨烯配合物的相对论自旋 - 轨道耦合（SOC）效应。CASPT2 - SOC方法揭示了铱与苯在1.81 Å距离处具有很强的结合亲和力（33.1 kcal mol⁻¹），这具有单参考特征，而在3.00 Å处具有较弱的结合亲和力（6.3 kcal mol⁻¹），具有多参考特征。在铱 - 石墨烯配合物中，铱原子的四重基态在吸附后变为二重态，并且optB86b - vdW - SOC泛函预测的结合能仍然很高（33.8 kcal mol⁻¹）。在所有情况下，动态相关效应都对结合有显著贡献。用杂化泛函HSE06计算的态密度表明，即使在标量相对论计算中，吸附的铱原子也会在石墨烯中诱导出0.3 eV的能隙，这与局域密度近似预测的金属行为相反。结果表明，强相关效应有助于被铱原子覆盖的石墨烯中带隙的打开。HSE06预测的磁各向异性能量值为0.1 kcal mol⁻¹，低于使用局域泛函计算的值。
