Molecular kondo problemfirst-principles approach for scanning-tunneling microscope studies

Resumen

Kondo resonances are ubiquitous in molecular electronics experiments and scanning tunneling microscopies of molecular adsorbates. Still, a common theoretical framework for understanding, interpretation and prediction of these experiments is lacking. This is attributed to the complexity of molecular systems, where common knowledge is likely to fail and atomistic ab-initio methods are needed. This work is hoped to be a contribution to the quest for a new feasible computational scheme for Kondo systems. We use the Wannier function method to transform the standard Kohn-Sham electronic structure to a localized basis set. This allows for a separation of electronic degrees of freedom as in the Anderson model. The method is firstly examined in the classical impurity problem: the cobalt impurity in the face-centered copper matrix. The second system of interest is a metal-organic molecule (copper phthalocyanine) adsorbed on the silver surface. The Wannier approach proves to be able to obtain molecular orbitals in the presence of the silver substrate. The study of molecule-substrate hybridization provides an important insight into the experimentally observed Kondo effect. A model Hamiltonian is proposed, which is solved in the non-crossing approximation. The spectral function obtained is directly related to the experimental differential conductance. Since the limitations of our approach are mostly given by the limitations of the underlying one-particle electronic structure (Kohn-Sham and local density approximation), we conclude that our approach presents a feasible way to simulate multi-orbital Kondo systems.