Gabin Treboux

Calcium phosphate clusters

The potential energy surfaces associated with [Ca3(PO4)2n clusters are analyzed in detail using ab initio calculations for n ranging from one to four. Considering separated clusters, energy criteria favor the so-called Posners cluster Ca9(PO4)6, which is the core of the actual structural model of amorphous calcium phosphate. This is rationalized through the existence of a distinct CaO bonding pattern in this cluster. Considering aggregated clusters as a possible model for amorphous calcium phosphate, the aggregation of Ca3(PO4)2 clusters appears as an alternative to Posners hypothesis.

Electronic conductance of helicenes

Abstract We report calculations of the electronic properties of helicene molecules. By tuning the radius of the helix and the width of the helix ribbon a helicene can be made semiconducting or metallic. We calculate the I / V characteristic for representatives of selected helicene classes, and analyse their ballistic electronic conductance. For a hybrid metal–semiconductor helicene we show localization of metallic states, and propose the design of a quantum dot based on this phenomenon.

Conductance in nanotube Y-junctions

Abstract We characterise the electronic properties of triangulenes and study their use as building blocks in nanotube metallic Y-junctions. We calculate the ballistic conductance of such junctions using the Landauer formalism, and identify the existence of a non-conduction energy window when the system has a C 3 axis centered on a six-membered ring. Such a system can exploit a local C 6 symmetry to stabilize the central region of the Y-junction, thereby opening a band gap.

Loss of translational symmetry in carbon nanotubes

Abstract The loss of translational symmetry at the ends of a carbon nanotube has a non-trivial effect on its ballistic conductance. Capping an armchair nanotube at one end leads to the loss of one ballistic conductance channel. This explains recent experimental findings of S. Frank, P. Poncharal, Z.L. Wang, W.A. de Heer [Science 280 (1998) 1744]. The loss of translational symmetry is not accompanied by the localization of states at the open ends of an armchair nanotube. This contrasts with the zigzag case where localized end-states do occur. This behavior derives from the properties of the corresponding infinite nanotubes.