1,720,997 research outputs found
LOCALIZATION PROPERTIES OF KRONIG-PENNEY INCOMMENSURATE POTENTIALS
No full textBy means of the renormalization approach we study the localization properties of a one-dimensional system of δ-like potential barriers, whose heights are modulated incommensurately with respect to their separation. We show how to distinguish different types of localized states present in the spectrum. Our study shows that in the case of slowly varying potential heights, the Lyapunov coefficient of exponentially localized states approaches zero linearly in correspondence to energies where a transition to power-law localized states is present. A second transition to extended states is then observed. The consequences on the transmittivity of the system are described
Beyond exponential localization in one-dimensional electrified chains
No full textWe interpret a new kind of localization in a finite one-dimensional tight-binding model under a weak applied electric field. This phenomenon is quite general and manifests itself in a more than exponential decreasing behaviour of the chain transmittivity. We provide analytic expressions for the transmittivity and confirm the theoretical results by transfer matrix numerical calculations. We show that this phenomenon is present in ordered as well as in aperiodic (incommensurate and pseudorandom systems) irrespective of the number of allowed bands
Electronic transport for random dimer-trimer model Hamiltonians
No full textIn this paper we study the transport properties of model chains constituted by random sequences of monomers, dimers, and trimers. We investigate the transmission properties of the random dimer model (RDM), where one of the two site energies of the lattice is assigned to couple of adjacent sites, while the other site energy has no constraints on its probability of occurrence. For comparison, we investigate the transport properties of other models of correlated disorder which can be considered as ``components'' of the RDM: the random dimer-isolated monomer, the random dimer-trimer model, and the random dimer alloy model, which is a binary alloy of dimers. Scaling laws of transmittivity with chain lengths are investigated
Electric-field effect on the transmittivity of aperiodic Kronig-Penney crystals
No full textWe describe the effect of a static and uniform electric field on the electronic transport properties of one-dimensional periodic and deterministic aperiodic systems described by the Kronig-Penney model. We study the crystal transmittivity as a function of the length of the sample and of the field strength. In the periodic case we interpret the results exploiting the tilted band scheme and point out regions with a more than exponential decreasing rate of transmittivity. In the case of an incommensurate slowly varying potential we interpret the fine structure of the transmittivity by means of a continuous approximation. In the pseudorandom case we confirm the delocalization effect of the field and we compare the results with the purely random case
Organic Electronic Materials: Conjugated Polymers and Low Molecular Weight Organic Solids
No full text
Ab initio molecular dynamics study of the structure of emeraldine base polymers
No full textWe present a Car-Parrinello molecular-dynamics study of the three-dimensional crystalline regions of the emeraldine base II polymer. Our results are compared with the structure obtained from experimental x-ray diffraction spectra and with similar calculations performed on an isolated infinite chain of the emeraldine base polymer. Environmental interchain effects are thus highlighted
Base and salt 3D forms of Emeraldine II polymers by Car-Parrinello molecular dynamics
No full textWe have studied structural and electronic properties of the three-dimensional crystalline regions of Emeraldine II polymers, in the base (EB-II) and salt (ES-II) forms, by means of first principle Car-Parrinello molecular dynamics. We compare the geometrical structures of the polymer chains in the primitive cells of EB-II and ES-II, pointing out the structural effects due to the protonation with HCl of the iminic nitrogens in the EB-II chains, and the effect of the counterions between neighboring chains. We also analyze the HOMO electron density distribution, band structure and density of states of the resulting bipolaronic structure of ES-II, which is energetically stable and maintains semiconductor character
- …
