Cobalt adatoms on graphene: Effects of anisotropies on the correlated electronic structure

Multiorbital electronic correlation effects of Co adatoms on graphene: An ionic Hamiltonian approach

“…More possibilities are found by using different functionals [8,13]. The electronic configurations found in the literature are 3d 9 4s 0 with total spin S = 1/2 [3,12], 3d 8 4s 1 with S = 3/2 [3,11,12] and an intermediate occupation of 7.5 in the d shell due to a dynamical hybridization with graphene [8]. In addition, a cluster calculation based on a wave-function approach [15] predicted the configurations 3d 9 4s 0 and 3d 7 4s 2 at Co-graphene distances of 1.6 and 3.1 Å, respectively.…”

“…The Co on graphene system has been the focus of many theoretical [8,[11][12][13][14][15][16][17] and experimental [6,18] works. The combination of the multiorbital features proper of the Co d valence shell and the particular characteristics of graphene electronic structure makes the system both interesting and challenging.…”

“…The theoretical description of this system is still under discussion. At the density functional theory (DFT) level, the most stable position is found to be at the hollow site, with an adsorption height of ≈1.5 Å with either generalized gradient (GGA) or local density (LDA) approximations [3,8,11,12,14,[19][20][21]. Nevertheless, when the GGA+U method [22] is used, the results are quite sensitive to the value of U .…”

“…Nevertheless, when the GGA+U method [22] is used, the results are quite sensitive to the value of U . For example, for U = 4 eV, the most stable position is on top at ≈1.8 Å [3,11,12,14]. More possibilities are found by using different functionals [8,13].…”

“…The most commonly used are probably the noncrossing and one-crossing approximations (NCA and OCA) [27][28][29], although the equations of motion (EOM) approach [30,31], used in the present work, provides a useful alternative [32][33][34][35]. In this context, the Co on graphene system was solved at several temperatures by using the GGA+OCA method [8] and recently by using both QMC and ED [11]. In addition, the system was analyzed by using a tight-binding approximation and a renormalization approach [12].…”