ELECTRON CORRELATION

Electron Correlation - The Electronic Ground State of Graphene Nanoribbons

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 Obiettivo del progetto (Objective)

'Graphene nanoribbons are derivates of graphene. Since its discovery in 2004 by Andre K. Geim and Konstantin S. Novoselov it has received enormous attention earning its discoverers the 2010 nobel prize. The great interest in graphene originates in its unique properties.

Graphene nanoribbons are an interesting building block for spintronics. In standard electronics the information carrier is the charge (the electron). When a charge current is present the signal is “on”, when there is no charge current the signal is “off”. In this setup the spin information (“up” or “down”) is completely ignored. Graphene nanoribbons, however, offer the possibility to add the spin degree of freedom to conventional electronic devices. The advantages are numerous.

It has been shown theoretically that electrons localise on the sides of nanoribbons. This electronic structure is reminiscent of the electronic structure of the H2 molecule at dissociation limit. The dissociated H2 molecule is the prototype system of static correlation. In this project recently developed theories and methods that accurately describe static correlation are applied to graphene nanoribbons. To investigate the electronic ground state structure with an efficient implementation of the theories and methods will be developed.

In this project Prof. Angel Rubio, scientist in charge and head of the nano bio Spectroscopy group at the at the Basque Country University (UPV/EHU) in San Sebastian, Spain, Prof. Gustavo Scuseria, head of the quantum chemistry group at Rice University in Houston, USA, and Dr. Daniel Rohr, researcher in the project, join forces to investigate the electronic structure of graphene nanoribbons. The project will be executed by Dr. Daniel Rohr. He will join the group in Spain for 24 months during which he will spend approximately 6 months in Houston.'

Introduzione (Teaser)

EU-funded scientists are joining forces to develop an accurate and efficient method to describe electron correlation in molecules.

Descrizione progetto (Article)

With an unconventional electronic structure, graphene holds great promise for spintronics applications. Research has shown that electrons localise on the sides of graphene nanoribbons. This electronic structure resembles that of the hydrogen molecule at dissociation limit, which is the prototype static correlation system.

In the EU-funded project 'Electron correlation - the electronic ground state of graphene nanoribbons' (ELECTRON CORRELATION), current theories and methods that accurately describe static correlation are applied to graphene nanoribbons. As static correlation is predominant in the molecule bond dissociation region, the project is expected to enhance understanding about bond cleavage and bond forming processes.

Combining density functional theory (DFT) and density matrix functional theory (DMFT), scientists developed short-range DFT and long-range DMFT. They extended the random phase approximation method to allow for spin-polarised or unrestricted calculations.

Small test system calculations revealed important new insights. The hydrogen molecule dissociation curve does not exhibit the highly discussed 'bump' at intermediate distances, but in contrast, energy saturates at physical bond distances. In addition, a fractional spin error has been observed at the dissociation limit.

ELECTRON CORRELATION is paving the way toward novel spintronics applications with significant implications for the electronics industry.