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The recent tremendous progress in man-made nanostructures has not been followed by similar advances in the development of suitable theoretical tools. In particular we still lack a powerful approach to describes both the realistic band-structure and correlation aspects equally well for strongly coupled nano-objects. Here we propose a new approach based on the recently introduced dynamical vertex approximation [1]. We demonstrate its reliability already on the one-particle vertex level by means of a detailed comparison with the exact solution for a small benzene ring, a case which can still be computed by means of a multi-site Quantum Monte Carlo solver. We then apply our method to the case of a larger nanoscopic system: a quantum point contact. One puzzling experimental observation is that the conductance through a metallic nanowire drops faster than exponentially with the distance between the atoms, as the wire gets stretched [2]. We model the two parts of the wire through a quantum point contact with 110 atoms attached to infinite left and right leads and calculate the conductance through it. We show that the quantum point contact becomes insulating already before entering the tunneling regime due to a local Mott-Hubbard transition occurring on the atoms which form the point contact. As a second case, we study a La0.5Ca0.5MnO3 nano-cluster from ab-initio, showing how our approach can be employed for challenging studies of nanostructured materials with strongly correlated electrons [3]. [1] A. Valli, G. Sangiovanni, O. Gunnarsson, A. Toschi and K. Held "Dynamical vertex approximation for nanoscopic systems" Physical Review Letters 104, 246402 (2010) [2] J. M. Krans, C. J. Muller, I. K. Yanson, Th. C. M. Govaert, R. Hesper and J. M. van Ruitenbeek "One-atom point contacts" Physical Review B 48, 14 721 (1993) [3] G. Sangiovanni, et al., in preparation |
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