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- Chakarova Käck, Svetla, 1977, et al.
(författare)
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Binding of polycyclic aromatic hydrocarbons and graphene dimers in density functional theory
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12, s. Art. Nr. 013017-
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Tidskriftsartikel (refereegranskat)abstract
- An early van der Waals density functional (vdW-DF) described layered systems (such as graphite and graphene dimers) using a layer-averaged electron density in the evaluation of nonlocal correlations. This early vdW-DF version was also adapted to approximate the binding of polycyclic aromatic hydrocarbons (PAHs) (Chakarova S D and Schröder E 2005 J. Chem. Phys. 122 054102). In parallel to that PAH study, a new vdW-DF version (Dion M, Rydberg H, Schröder E, Langreth D C and Lundqvist B I 2004 Phys. Rev. Lett. 92 246401) was developed that provides accounts of nonlocal correlations for systems of general geometry. We apply here the latter vdW-DF version to aromatic dimers of benzene, naphthalene, anthracene and pyrene, stacked in sandwich (AA) structure, and the slipped-parallel (AB) naphthalene dimer. We further compare the results of the two methods as well as other theoretical results obtained by quantum-chemistry methods. We also compare calculations for two interacting graphene sheets in the AA and the AB structures and provide the corresponding graphene-from-graphite exfoliation energies. Finally, we present an overview of the scaling of the molecular–dimer interaction with the number of carbon atoms and with the number of carbon rings.
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- Kleis, Jesper, 1974
(författare)
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First-principles calculations of polymer interactions
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports on studies of interactions in sparse matter by first-principles calculations, in particular polymeric systems. The focus is on the three unbranched simple polymers: polyethylene (PE), isotactic polypropylene (PP) and isotactic polyvinylchloride (PVC), which together represent an important class of materials that form complexes stabilized by weak but long-range dispersive interactions. The latter ones are not included in traditional density functional theory (DFT). Due to the missing nonlocal description traditional implementations of DFT predicts, e.g., the PEcrystal to be unstable, contradicting both experiments and intuition.Two schemes are applied which extend the applicability of DFT to such sparse systems:1. A systematic correction scheme that applies to parallel well-separated polymers is proposed. From the length-averaged electron densities of the polymers and their static polarizabilities, both calculated with the traditional DFT, the dynamic response and in turn the asymptotic dispersive interaction of the polymers are modeled. Simple expressions for the orientation dependent polymerpolymer interaction energy are obtained, and even simpler expressions are found by enforcing the polymers to be cylindrically symmetric. Explicit results are given for PE, PP, PVC.2. The nonlocal correlation energy for pairs of PE-molecules is calculated also for short and intermediate separations using the recently developed general geometry (gg) DFT scheme [Phys. Rev. Lett. 92, 246401, 2004]. The gg-scheme models the electrodynamic response on the basis of the electron density only and applies also at binding distance and out. This allows us to calculate the cohesive energy landscape for the PE crystal, showing promising agreement with experimental values for equilibrium lattice constants.For well separated PE-chains (center-to-center distance > 8 Å) the two approaches turn out to be consistent with each other.
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- Kleis, Jesper, 1974
(författare)
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Van der Waals density-functional description of polymers and other sparse materials
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymers are abundant in nature --- rubber, tar and latex have been known to mankind for thousands of years. Early in the 20th century, a systematic synthesis of polymers was developed, but the great potential of synthesized polymers was recognized first during World War II. Since then,polymeric materials of enormous variety have been developed and constructed, and research has been devoted to improve the production and to develop new polymeric materials. A prediction of the materials behavior of such complex systems requires insight at all length scales. Proper microscopic quantum-mechanical calculations are prerequisites but out of reach of covering all length scales.As a first step in the direction of such a general description, we treat one of the simplest polymer systems by help of first-principles density-functional theory (DFT) calculations. Specifically, interactions of chains of simple linear nonbranched polyethylene (PE) are investigated. PE represents an important classof systems that form complexes stabilized by weak butlong-ranged dispersive interactions. Traditional DFTdoes not include the latter and predicts the PE crystal to be unstable, contradicting both experiments and intuition.A recently proposed density functional (vdW-DF), with aconsistent account of the dispersive interactions for general geometries [Phys. Rev. Lett. {\bf 92}, 246401, 2004], is implemented to infinite crystalline systems and applied to crystalline PE. The vdW-DF does not only lead to a stable PE crystal structure but also predictscrystal-parameter values in promising agreement withexperimental data. This motivates our application ofvdW-DF to other technologically important sparse-matter systems, including dimers of parallel PE, PP, and PVC polymers, hydrogen and potassium intercalation in graphite and bundles of nanotubes.The adopted first-principles methods are based on electron-structure calculations and differ significantly from the simplified force-field approaches. These have potential parameters fitted to experimental data at theequilibrium separation and are widely used for complex polymer systems. Here they are explicitly shown to give general intermolecular parameters that lack any solid physical foundation, and which thus has no guaranteed success for systems outside the training set or at separation beyond the equilibrium separation.The first-principles insight gained makes possible aa well-founded interatomic description and in turn better predictive power of these fast force-field schemes.
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