The electronic structure and magnetic properties of a single Fe adatom on aCuN surface have been studied using density functional theory in the local spindensity approximation (LSDA), the LSDA+U approach and the local densityapproximation plus dynamical mean-field theory (LDA+DMFT). The impurity problemin LDA+DMFT is solved through exact diagonalization and in the Hubbard-Iapproximation. The comparison of the one-particle spectral functions obtainedfrom LSDA, LSDA+U and LDA+DMFT show the importance of dynamical correlationsfor the electronic structure of this system. Most importantly, we focused onthe magnetic anisotropy and found that neither LSDA, nor LSDA+U can explain themeasured, high values of the axial and transverse anisotropy parameters.Instead, the spin excitation energies obtained from our LDA+DMFT approach withexact diagonalization agree significantly better with experimental data. Thisaffirms the importance of treating fluctuating magnetic moments through arealistic many-body treatment when describing this class of nano-magneticsystems. Moreover, it facilitates insight to the role of the hybridization withsurrounding orbitals.
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