Electronic Structures of Antisite Defects in Chiral (6,2) SiC Nanotubes

Antisite defects are common defects in nanotube materials and have seriously impacts on their electronic properties. Based on density-functional theory calculations, the electronic structures of the antisite defective chiral (6, 2) SiCNTs are investigated. C antisite and Si antisite lead to the formation of a depression and a bump in the surface of the nanotube, respectively. In the band gap of the SiCNT with a C antisite defect, the occupied level near the top of the valence band is formed, while the unoccupied level originating from the Si antisite defect enters the conduction band of the SiCNT.

Levallois Tradition epigones in the Middle Nile Valley: survey in the Affad Basin

The paper presents the results of an archaeological ground survey aimed to record prehistoric settlement landscape in chosen parts of the Southern Dongola Reach (Tergis, Affad and El-Nafab districts). The project fills in the gaps in earlier research on the right bank of the Nile. Numerous new sites were recorded, all reflecting a frequently occupied level of silts and sands originating in the former river valley aggradations. Prospection of locations recorded in 2003 and later demonstrated also the progressing destruction of archaeological sites on the fringes of modern settlement and the new road from Karima to Nawa.

MESOSCOPIC ORBITAL MAGNETISM IN AN INTEGRABLE SYSTEM

We study the mesoscopic orbital magnetism of a free electron gas in a rectangular box in the zero-temperature limit. We find that, as in weakly disordered systems, it can be well-described by the van Vleck susceptibility that couples just two size-quantized energy levels: the Fermi (last occupied) level and the first unoccupied level. Large fluctuations of the off-diagonal matrix elements of the angular momentum and, more importantly, of the nearest level spacings — level bunching characteristic of classically integrable systems — are responsible for the absence of effective self-averaging in this system. We develop a detailed analytical description and conduct extensive numerical simulations based on a combined averaging over the energy spectrum, and over the aspect ratio of rectangles with equal areas.

Electronic Structure of Doped Buckminsterfullerene

ABSTRACTMolecular cluster calculations within the local density approximation have been performed in a study of the electronic structure of the C60 molecule - “Buckminsterfullerene” doped with K, B and N. Calculations for the KC60 molecule, with the K atom located at the centre of the cage as well as at different positions inside or outside the cage, show how the valence 4s electron is transferred to the LUMO state of the bare C60 molecule. Doping with a B or N atom located at the centre of the cage creates a molecule with a partly occupied level of 2p character in the HOMO and LUMO gap, similar to donor and acceptor levels in the band gap of traditionally doped semiconductors. Doping by substitution of one or two of the carbon atoms in the cage with X = B or N, as modelled with the C59 X1 or C58X2 clusters, gives a different structure with a splitting of the HOMO and LUMO levels in the pure C60 molecule and with the creation of acceptor and donor levels with the substitution of B and N, respectively.