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

Abstract

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 (C${}_{24}$H${}_{12}$). 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 $3d^{7}4s^2$ ($S=3/2$) 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 eV. We analyze the obtained results in terms of a simple model Hamiltonian that involves Coulomb repulsion ($U$) and exchange coupling ($J$) parameters for the 3$d$ shell of Co, which we estimate from first-principles calculations. We show that while the exchange interaction remains constant upon adsorption ($\simeq 1.1$ eV), the Coulomb repulsion significantly reduces for decreasing distances (from 5.3 to 2.6$\pm$0.2 eV). The screening of $U$ favors higher occupations of the 3$d$ 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.

12 pages, 6 figures, 2 tables

References in corpus (14)

• The electronic properties of graphene
• Emergence of magnetism in graphene materials and nanostructures
• Limits on intrinsic magnetism in graphene
• Monovalent impurities on graphene: midgap states and migration barriers
• Theory of quasiparticle spectra for Fe, Co, and Ni: bulk and surface
• Maximally Localized Wannier Functions within the FLAPW formalism
• Localized Spins on Graphene
• Metal adatoms on graphene and hexagonal boron nitride: Towards the rational design of self-assembly templates
• Orbital selective and tunable Kondo effect of magnetic adatoms on graphene: Correlated electronic structure calculations
• Gate-controlled Kondo screening in graphene: Quantum criticality and electron-hole asymmetry
• Adsorption of diatomic halogen molecules on graphene: A van der Waals density functional study
• Graphene adhesion on mica: Role of surface morphology
• Modeling vacancies and hydrogen impurities in graphene: A molecular point of view
• Correlated electrons in Fe-As compounds: a quantum chemical perspective

Cited by in corpus (2)

• The Physics of Kondo Impurities in Graphene
• Ab Initio Many-body Study of Cobalt Adatoms Adsorbed on Graphene