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First-principle simulations of electronic structure in semicrystalline polyethylene
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. ABB Corporate Research, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 20, 204901Article in journal (Refereed) Published
Abstract [en]

In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (similar to 0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even belowthe mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017. Vol. 146, no 20, 204901
National Category
Chemical Sciences Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-208802DOI: 10.1063/1.4983650ISI: 000401778900042Scopus ID: 2-s2.0-85019720001OAI: oai:DiVA.org:kth-208802DiVA: diva2:1108961
Funder
Swedish Research Council, 621-2012-2673 621-2014-5398VINNOVA, 2015-06557
Note

QC 20170613

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-06-13Bibliographically approved

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Moyassari, AliUnge, MikaelHedenqvist, Mikael S.Gedde, Ulf W.Nilsson, Fritjof
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Polymeric MaterialsFibre and Polymer Technology
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