Dr. Pierre Hirel


Master 2nd year Research Project, Uni. Rennes 1 (France)
Jan.-June 2005

This research project lasted for the whole second semester of the second year of the Master of Physics. It was performed in the GMCM under the supervision of Dr. Brice Arnaud, with whom I shared a great interest in nanotubes and their fascinating properties. The project was entitled "Theoretical study of electronic and optical properties of boron nitride nanotubes".

We performed ab initio simulations in order to obtain informations on electronic band structure and optical response of hexagonal boron nitride (hBN). This material is ionic, and we calculated the charge transfer by using the Bader electronic basins analysis. BN also presents strong excitonic effects, which play a great role in its optical response. Hence we used the GW approximation to study the excited states of the material, and calculated the optical spectrum by solving the Bethe-Salpeter equation. Then we compared these results with a tight-binding model that we developped.

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hBN electronic band structure as calculated with PAW (black lines), and compared with tight-binding model (red triangles) and with a vacuum cell (blue dots).

In a second part, we performed ab initio calculations to determine the electronic properties of a BN nanotube, the "armchair" nanotube (4,4). The relaxation of this nanotube shows that, because of the ionicity of the bonds, the atoms of bore and nitride are slightly pulled apart, and form two cylinders of different electric charges.

Nanotube BN

The BNNT (4,4), of armchair type.

The manuscript of this project is available here (in French).

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