Multiplets in single Fe-phthalocyanine molecule on MgO(001)

A challenge to miniaturize devices for novel magnetic application now extends to treating the extreme limit of a single atom or molecule. For molecules with transition-metals (TM), multiplet (or electronic configuration) of the $d$-electrons is an essential aspect in the electronic properties. Further, understandings of molecule-substrate interactions [1] are of crucial importance toward single-molecule-based applications. Previously [2], we demonstrated the utility of the FLAPW method based on the constraint DFT for determining the ground state of the $^{\mathrm{3}}$A$_{\mathrm{2g}}$ electronic configuration in a single FePc molecule. We here address our investigation to treat a single FePc on a MgO(001) substrate. The HOMO and LUMO states, governed by the Fe 3$d$-orbitals of the FePc molecule, clearly remains in the MgO band gap as seen in the isolated molecule, which gives rise to the ground state of the $^{\mathrm{3}}$B$_{\mathrm{2g}}$ electronic configuration. The transition in the electronic configurations is explained by a weak hybridization between the Fe $d_{\mathrm{z2}}$ and O $p_{\mathrm{z}}$ orbitals at the molecule-substrate interface. [1] S. Nakashima et al., Jpn. J. Appl. Phys. \textbf{52}, 110115 (2013). [2] K. Nakamura et al., Phys. Rev. B \textbf{85}, 235129 (2012).