Browsing by Subject "Electronic structure calculations"

Now showing 1 - 2 of 2

Open Access
Ab initio study of hydrogenic effective mass impurities in Si nanowires
(Institute of Physics Publishing, 2017-01) Peelaers, H.; Durgun, Engin; Partoens, B.; Bilc, D. I.; Ghosez, P.; Van De Walle C. G.; Peeters, F. M.
The effect of B and P dopants on the band structure of Si nanowires is studied using electronic structure calculations based on density functional theory. At low concentrations a dispersionless band is formed, clearly distinguishable from the valence and conduction bands. Although this band is evidently induced by the dopant impurity, it turns out to have purely Si character. These results can be rigorously analyzed in the framework of effective mass theory. In the process we resolve some common misconceptions about the physics of hydrogenic shallow impurities, which can be more clearly elucidated in the case of nanowires than would be possible for bulk Si. We also show the importance of correctly describing the effect of dielectric confinement, which is not included in traditional electronic structure calculations, by comparing the obtained results with those of G0W0 calculations.
Open Access
Structural and electronic properties of carbon-based materials
(2000) Kılıç, Çetin
In this thesis, some carbon-based materials in nano scale have been investigated by using first-principles methods as well as transferable tight-binding and empirical potential models. The focus of interest has been in the cubane molecule among cage-like structures and in the carbon nanotubes among graphite-related materials. The first-principles calculations predict that cubane-like structures can exist for other group IV elements such as Si and Ge. The energetics and dynamics of such molecules has been studied. By performing quantum molecular dynamics simulations at high temperature a deformation path from cubane to cyclooctatetraene has been established. For solid cubane the structural and electronic properties and doping by alkali metal atoms have been studied. In the study of carbon nanotubes under pressure some new carbon forms due to covalent bonding between the neighboring tubes has been identified. It has been shown that the electronic structure of single wall carbon nanotubes is affected by radial deformations. For example, some zigzag nanotubes have been found to experience semiconductor-to-metal transition as a result of compression. Exploiting this property, it has been shown that variable and reversible quantum structures can be realized on a single carbon nanotube. Finally, other quantum structures which can lead to novel nano-scale molecular devices have been proposed.