Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 27: Graphene II

O 27.6: Talk

Tuesday, March 27, 2012, 11:45–12:00, MA 041

Role of electron correlations in cobalt adsorption on graphene: A quantum chemical perspective — •Alexander Rudenko and Frerich Keil — Hamburg University of Technology, Chemical Reaction Engineering, Eißendorfer Str. 38, D-21073 Hamburg, Germany

Correct theoretical description of transition metal (TM) complexes represents a challenging task due to the presence of strong electron correlations. Commonly used theoretical concepts, such as DFT or single-determinant (HF-based) approaches are often unreliable even in terms of qualitative description of these systems. In the present work we investigate the adsorption of a single cobalt atom on graphene within the finite cluster approach by means of the complete active space SCF approach (CASSCF), additionally corrected by the second-order perturbation theory. We construct the active space by considering 3d, 4s, and 4p cobalt orbitals as well as two pairs of the most relevant π and π^* surface orbitals. In contrast to standard DFT studies, we find that the Co adatom physisorbs on graphene without formation of any chemical bonds. As a result, the spin state of adsorbed Co remains to be the same as for the free cobalt atom, i.e., S=3/2. The ground orbital configuration changes, however, from 3d⁷4s² to 3d⁸4s¹ as Co approaches the surface. These results are in qualitative agreement with the LDA+U and hybrid-functional calculations, which really indicate an important role of the Coulomb repulsion in the bonding and electronic properties of Co on graphene. In addition, we analyze the obtained CASSCF results in terms of a simple model Hamiltonian.