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Theory and computations of low dimensional materials

Gian Paolo Brivio

The main interest of the Group is to develop and interpret first-principle investigations of electronic properties of novel low dimensional materials. The Group is a core node partner of the European Theoretical Spectroscopy Facility (ETSF) which comprises fourteen  EuropeanUniversities and Laboratories and whose aim is the advance of computational spectroscopy. In our studies we make use of (and contribute to) a plane-wave supercell code and of an embedding one, both within density functional theory (DFT), and of localized basis set codes to work out conductance properties through molecular junctions and interfaces. All these results are of perspective applications in nano-electronic and photovoltaic devices.


Core-level spectroscopy

The near edge x-ray absorption fine structure (NEXAFS) of aromatic molecules like pentacene, a recurring ingredient in organic electronic devices, was computed by first principles as a function of the photon polarization vector of a linearly polarized X-ray beam. We highlighted and explained a splitting in energy for absorption peaks relative to the various polarization directions. Such an effect can be used to determine the orientation of the molecular plane in the condensed phase, as well as of the molecules within that plane, as confirmed by experiments at the ELETTRA synchrotron.

Magnetic nanostructures

The electronic and structural properties of a one-layer thick chromium oxide grown on an iron substrate was characterized by first-principle simulations, together with scanning tunneling microscopy and Auger experiments performed at Politecnico di Milano. We have identified the magnetic state of the system to be antiferromagnetically coupled with the substrate and highlighted the reasons beyond the characteristic surface structures observed as a function of chromium coverage.

Molecular circuits

We have computed the conductance of an hydrogen molecule embedded within copper contacts under the application of an external bias, as it occurs in single molecule break junction experiments. The dependence of the conduction channels on the junction elongation and on molecular dissociation at the contact was determined.