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- Langreth, D. C., et al.
(författare)
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A density functional for sparse matter
- 2009
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 21:8, s. 084203-
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Tidskriftsartikel (refereegranskat)abstract
- Sparse matter is abundant and has both strong local bonds and weak nonbonding forces, in particular nonlocal van der Waals (vdW) forces between atoms separated by empty space. It encompasses a broad spectrum of systems, like soft matter, adsorption systems and biostructures. Density-functional theory (DFT), long since proven successful for dense matter, seems now to have come to a point, where useful extensions to sparse matter are available. In particular, a functional form, vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401; Thonhauser et al 2007 Phys. Rev. B 76 125112), has been proposed for the nonlocal correlations between electrons and applied to various relevant molecules and materials, including to those layered systems like graphite, boron nitride and molybdenum sulfide, to dimers of benzene, polycyclic aromatic hydrocarbons (PAHs), doped benzene, cytosine and DNA base pairs, to nonbonding forces in molecules, to adsorbed molecules, like benzene, naphthalene, phenol and adenine on graphite, alumina and metals, to polymer and carbon nanotube (CNT) crystals, and hydrogen storage in graphite and metal–organic frameworks (MOFs), and to the structure of DNA and of DNA with intercalators. Comparison with results from wavefunction calculations for the smaller systems and with experimental data for the extended ones show the vdW-DF path to be promising. This could have great ramifications.
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- Langreth, D. C., et al.
(författare)
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Van der Waals Density Functional Theory with Applications
- 2005
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 101:5, s. 599-610
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Tidskriftsartikel (refereegranskat)abstract
- The details of a density functional that includes van der Waals (vdW) interactions are presented. In particular we give some key steps of the transition from a form for fully planar systems to a procedure for realistic layered compounds that have planar symmetry only on large-distance scales, and which have strong covalent bonds within the layers. It is shown that the random-phase approximation of that original functional can be replaced by an approximation that is exact at large separation between vdW interacting fragments and seamless as the fragments merge. An approximation to the latter which renders the functional easily applicable and which preserves useful accuracy in both limits and in between is given. We report additional data from applications to forms of graphite, boron nitride, and molybdenum sulfide not reported in our previous communication.(C) 2004 Wiley Periodicals, Inc.
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- Rydberg, Henrik, 1968, et al.
(författare)
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Hard numbers on soft matter
- 2003
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Ingår i: SURFACE SCIENCE. ; 532, s. 606-
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Tidskriftsartikel (refereegranskat)
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| 8. |
- Rydberg, Henrik, 1968
(författare)
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Nonlocal Correlations in Density Functional Theory
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Density Functional Theory, the widely used local and semilocal approximations to the exchange-correlation energy, the local density approximation (LDA) and the generalized gradient approximations (GGAs), lack a physical description of truly nonlocal correlation effects, which are absolutely essential for a proper description of soft matter. A scheme is proposed that provides a basis for systematic improvements beyond LDA and GGA, including correlations at intermediate and long range, giving rise to bonds of pure van der Waals type as well as more intricate, intermediate-range correlation bonds. The scheme is developed with regard to computational efficiency as well as physical soundness, and incorporated into the standard DFT formalism. The method is applied to a generic set of systems, illuminating different aspects of nonlocal correlations. Studies of van der Waals interactions in molecules, of nonlocal correlations between surfaces, and of bonds in graphite and between graphene layers are included. Successful account of energetics, bond lengths and compressibilities of graphitic systems clearly illustrates the significance of using approximate exchange-correlation energy functionals that are based on the true physics of the system. Finally an explicit formula is given for a general nonlocal correlation density functional, suitable for incorporation into standard DFT schemes.
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