The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticle in its vicinity, leading to a (partially) screened spin state. Here, we use the flexibility of Fe-porphin (FeP) molecules adsorbed on a Pb(111) surface to reversibly and continuously tune between these distinct ground states. We find that the FeP moment is screened in the pristine adsorption state. Approaching the tip of a scanning tunneling microscope, we exert a sufficiently strong attractive force to tune the molecule through the quantum phase transition into the free-spin state. We ascertain and characterize the transition by investigating the transport processes as function of tip-molecule distance, exciting the YSR states by single-electron tunneling as well as (multiple) Andreev reflections. arXiv:1807.01344v2 [cond-mat.mes-hall]

The surface-assisted intramolecular ligand reaction of a porphyrin molecule adsorbed on Au(111) is studied by scanning tunneling microscopy and spectroscopy. The temperature-induced stepwise transformation of iron octaethylporphyrin proceeds via a concentric electrocyclic ring closure, with the final product iron tetrabenzoporphyrin being identified by its characteristic Kondo resonance. Along with the transformation of the organic ligand, changes in the magnetic fingerprint are observed, indicating an increasing coupling of the iron spin with the substrate electrons.

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An extended group function model has been applied to determine the interatomic potential for the X1 Sigma state of ArLi+. By adopting a (14s, 10p, 7d, 4f, 1g/7s, 5p, 3d, 2f, 1g) contracted Gaussian type basis set, the following potential minimum parameters are obtained: Re=4.50 au and De=10.569 mHartree. On the basis of an error analysis it is concluded that the calculated binding energy is in error by no more than 0.3%. The accuracy of the potential is superior to previously determined potentials.

Using magnetic endohedral fullerenes for molecular spintronics requires control over their encapsulated magnetic moments. We show by field-dependent x-ray magnetic circular dichroism measurements of Gd3N@C80 endohedral fullerenes adsorbed on a Cu surface that the magnetic moments of the encapsulated Gd atoms lie in a 4f7 ground state and couple ferromagnetically to each other. When the molecules are in contact with a ferromagnetic Ni substrate, we detect two different Gd species. The more abundant one couples antiferromagnetically to the Ni, whereas the other one exhibits a stronger and ferromagnetic coupling to the substrate. Both of these couplings to the substrate can be explained by an indirect exchange mechanism mediated by the carbon cage. The origin of the distinctly different behavior may be attributed to different orientations and thus electronic coupling of the carbon cage to the substrate, as revealed by scanning tunneling microscopy of the fullerenes on Cu.

A set of computational models, denoted extended group function models, are introduced for describing intermolecular interactions of closed shell systems. The models have the following properties: They have a conceptual structure which facilitates interpretation. The models can be applied for any intersystem distances. The models are size extensive. The basis set superposition error can be eliminated at the correlation level. The models are computationally efficient. A test calculation is performed on the complex Ne⋅Li+.