1,721,022 research outputs found
Ab initio investigation of hybrid organic-inorganic perovskites based on tin halides
No full textThe structural and electronic properties of both inorganic and hybrid organic-inorganic perovskites based on tin halides are investigated from the first principles. In particular, we contrast the inorganic CsSnCl(3) and CsSnI(3) to their hybrid counterparts (CH(3)NH(3))SnCl(3), (CH(3)NH(3))SnI(3), and (NH(2)CH=NH(2))SnI(3), which were obtained by substituting the inorganic Cs cation with the methylammonium CH(3)NH(3) and the formamidinium NH(2)CH=NH(2) cations. The comparison between the hybrid perovskites and the inorganic counterparts sheds light on the effects of the filling molecule on the structural and electronic properties of the compound. We show that the stability against the distortion of the perovskitic cage strongly depends on the embedded cation. The electronic properties (in particular, the band gap) can be tuned by a suitable choice of the organic molecule, and, in particular, of its size
Ab initio investigation of the structural and electronic properties of TiO2 nanostructures
No full textELECTRON-ELECTRON CORRELATION IN SILICON ANISOTROPIC QUANTUM DOTS
No full textIn this paper we study the electron-electron correlation in silicon anisotropic quantum dots. A variational approach to the problem of the quantum confinement of two electrons in an ellipsoidal quantum dot is presented. All the calculations are done as a function of the dot aspect ratio, showing how the Coulomb repulsion and dielectric effects (related to the dielectric mismatch between the dot and the surrounding medium) give rise to shape-dependent correlation effects. The energy needed to add a second electron to the ellipsoidal quantum dot is calculated and discussed as well
Interplay between quantum confinement and electron-electron interaction in deformed silicon quantum wires
No full textIn this paper we investigate quantum confinement and electron-electron correlation in silicon deformed quantum wires. Starting from the single-particle picture, which shows the possibility of localizing one electron inside the wire deformation, we build a variational ansatz for the two-electron ground state. We compare the localizing effect induced by the deformation with the Coulomb repulsion, pointing out the existence of a two-electron confined ground state, depending on the wire geometry. On varying the geometrical parameters characterizing the wire deformation, it is possible to switch from structures dominated by the localization to structures in which the increase of the available volume makes the Coulomb contribution very relevant, as for ordinary quantum dots. The effects induced by the dielectric mismatch between the wire and the surrounding medium are included and discussed
Electronic properties and Schottky barriers at ZnO-metal interfaces from first principles
No full textFirst principles calculations were performed to study the interface electronic structure and the Schottky barrier heights (SBHs) of ZnO???metal interfaces. Different kinds of metals were considered with different chemistries on the polar (0 0 0 1) and (0 0 0 ̄1) ZnO surfaces. The projection of the density of states on the atomic orbitals of the interface atoms reveals that two kinds of interface electronic states appear: states due to the chemical bonding which appear at well defined energies and conventional metal-induced gap states associated with a smooth density of states in the bulk ZnO band gap region. The relative weight and distribution of the
two classes of states depend on both the ZnO substrate termination and on the metal species. SBHs are found to be very sensitive to the specific interface chemical bonding. In particular, it
is possible to note the occurrence of either Schottky barriers or Ohmic contacts. Our results have been compared with experiments and with available phenomenological theories, which estimate the SBH from few characteristic material parameters. Finally, the electronic and structural contributions to the SBH have been singled out and related to the different charge transfers occurring at the different interfaces
CONDUCTION-BAND ANISOTROPY EFFECTS IN SPHERICAL SEMICONDUCTOR NANOCRYSTALS: A THEORETICAL STUDY
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