Effect of the Quantum Zero-Point Atomic Motion on the Optical and Electronic Properties of Diamond and Trans-Polyacetylene (original) (raw)
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The European Physical Journal B, 2012
It has been recently shown, using ab-initio methods, that bulk diamond is characterized by a giant band-gap renormalization (∼ 0.6 eV) induced by the electron-phonon interaction. This result casts doubt on the accuracy of purely electronic calculations. In this work we show that in polymers, compared to bulk materials, due to the larger amplitude of the atomic vibrations the real excitations of the system are composed by entangled electron-phonon states. We prove as the charge carriers are fragmented in a multitude of polaronic states leading, inevitably, to the failure of the electronic picture. The presented results lead to a critical revision of the state-of-the-art description of carbon-based nanostructures, opening a wealth of potential implications.
Surface Science, 2007
Low dimensional systems, such as nanodots, nanotubes, nanowires, have attracted great interest in the last years, due to their possible application in nanodevices. It is hence very important to describe accurately their electronic and optical properties within highly reliable and efficient ab-initio approaches. Density functional theory (DFT) has become in the last 20 years the standard technique for studying the ground-state properties, but this method often shows significant deviations from the experiment when electronic excited states are involved. The use of many-body Green's functions theory, with DFT calculations taken as the zero order approximation, is today the state-of-the-art technique for obtaining quasi-particle excitation energies and optical spectra. In this paper we will present the current status of this theoretical and computational approach, showing results for different kinds of low dimensional systems.
arXiv: Materials Science, 2013
In this paper we investigate from first principles the effect of the electron-phonon interaction in two paradigmatic nanostructures: trans-polyacetylene and polyethylene. We found that the strong electron-phonon interaction leads to the appearance of complex structures in the frequency dependent electronic self-energy. Those structures rule out any quasi-particle picture, and make the adiabatic and static approximations commonly used in the well-established Heine Allen Cardona (HAC) approach inadequate. We propose, instead, a fully ab-initio dynamical formulation of the problem within the Many Body Perturbation Theory framework. The present dynamical theory reveals that the structures appearing in the electronic self-energy are connected to the existence of packets of correlated electron/phonon states. These states appear in the spectral functions even at T=0,KT=0\,KT=0,K, revealing the key role played by the zero point motion effect. We give a physical interpretation of these states by dis...
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Journal of Materials Science, 2012
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In this chapter, we present a study on the electronic properties of diamond carbon, using band structure and density of states calculations. The calculations are based on the use of the grid-based projector-augmented wave (GPAW) and atomic simulation environment (ASE) methods. The main results of our work are the optimization of diamond energy (to À17.57 eV) and the calculation of the gap with the PBE (Perdew, Burke, and Ernzerhof) and the functional hybrid PBE0 hybrid functional, which is about 5.368 eV (the closest value to the value found in the literature). We were also able to reproduce the experimental value of the lattice constant of diamond to within 0.2% for PBE0 and 0.4% for PBE. Our results contribute to the study of the electronic properties of diamond using GPAW and ASE simulation, which is a set of Python modules, designed to facilitate the setup, execution, and analysis of atomic/electronic calculations. This tight integration of ASE and GPAW should be exploited in future research of the electronic properties of diamond, which is one of the most promising materials for the integrated electronic and photonic, radio, optoelectronic, and quantum devices industry. This chapter provides interesting information for the theoretical and experimental communities working in this field.
Molecular Mechanics Interaction Models for Optical Electronic Properties
Journal of Computational and Theoretical Nanoscience, 2009
Molecular mechanics models for representing the response of a molecular charge distribution to an external electric field are discussed. The point dipole interaction model for calculating molecular polarizabilities and hyperpolarizabilities is reviewed. Its basic theory is presented and extensions including damping of interatomic interactions and the frequency-dependence are discussed. The presentation of results includes the polarizability, second hyperpolarizability and macroscopic polarization of a variety of systems including carbon fullerenes and fullerene clusters, carbon and boron nitride nanotubes, and proteins. , and he spent seven years in Denmark (whereof three years as postdoc with Professor Kurt V. Mikkelsen) before he moved to Norway in 2002. His research interests include the construction of molecular mechanics models for intermolecular forces, reactive force fields and optical properties, with applications in optics, nanoscience, catalysis and breakdown of dielectric liquids. He has published 70 papers in international journals with a referee system, he has more than 1600 citations and his H-index is 25.