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| 2. |
- Arpaia, Riccardo, 1985, et al.
(author)
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Untwinned YBa2Cu3O7-delta thin films on MgO substrates: A platform to study strain effects on the local orders in cuprates
- 2019
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In: Physical Review Materials. - 2475-9953. ; 3:11
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Journal article (peer-reviewed)abstract
- We have grown untwinned YBa2Cu3O7-delta (YBCO) films on (110) MgO substrates that were preannealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.
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| 3. |
- Barker, David, 1993, et al.
(author)
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Filter function of graphene oxide: Trapping perfluorinated molecules
- 2020
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 152:2
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Journal article (peer-reviewed)abstract
- We need clean drinking water, but current water purification methods are not always sufficient. This study examines the binding and binding mechanisms when graphene oxide is used as a filter material for removing perfluorinated substances and trihalomethanes. We use density functional theory calculations to examine the binding of the harmful molecules on graphene oxide. Our results indicate that the binding energies between graphene oxide and the investigated molecules are in the range of 370-1450 meV per molecule, similar to the binding energies obtained in other studies, where adsorption of similar size molecules onto graphene oxide has been investigated. This indicates that graphene oxide has the potential to separate the molecules of interest from the water. Significant contribution to the binding energies comes from the van der Waals (dispersion) interaction between the molecule and graphene oxide, while the hydrogen bonding between the functional groups of graphene oxide and the hydrogen atoms in functional groups on the molecules also plays a role in the binding.
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| 4. |
- Berland, Kristian, 1983, et al.
(author)
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A van der Waals density functional study of adenine on graphene: Single-molecular adsorption and overlayer binding
- 2011
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In: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23, s. 135001-
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Journal article (peer-reviewed)abstract
- The adsorption of an adenine molecule on graphene is studied using a first-principles van der Waals functional, vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401). The cohesive energy of an ordered adenine overlayer is also estimated. For the adsorption of a single molecule, we determine the optimal binding configuration and adsorption energy by translating and rotating the molecule. The adsorption energy for a single molecule of adenine is found to be 711 meV, which is close to the calculated adsorption energy of the similarly sized naphthalene. On the basis of the single-molecular binding configuration, we estimate the cohesive energy of a two-dimensional ordered overlayer. We find a significantly stronger binding energy for the ordered overlayer than for single-molecule adsorption.
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| 5. |
- Berland, Kristian, 1983, et al.
(author)
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Harris-type van der Waals density functional scheme
- 2013
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 88:4
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Journal article (peer-reviewed)abstract
- Biomolecular systems that involve thousands of atoms are difficult to address with standard density functional theory (DFT) calculations. With the development of sparse-matter methods such as the van der Waals density functional (vdW-DF) method [M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)], it is now possible to include the dispersive forces in DFT which are necessary to describe the cohesion and behavior of these systems. vdW-DF implementations can be as efficient as those for traditional DFT. Yet, the computational costs of self-consistently determining the electron wave functions and hence the kinetic-energy repulsion still limit the scope of sparse-matter DFT. We propose to speed up sparse-matter calculations by using the Harris scheme [J. Harris, Phys. Rev. B 31, 1770 (1985)]; that is, we propose to perform electronic relaxations only for separated fragments (molecules) and use a superposition of fragment densities as a starting point to obtain the total energy non-self-consistently. We evaluate the feasibility of this approach for an adaption of the Harris scheme for non-self-consistent vdW-DF (sfd-vdW-DF). We study four molecular dimers with varying degrees of polarity and find that the sfd scheme accurately reproduces standard non-self-consistent vdW-DF for van der Waals dominated systems but is less accurate for those dominated by polar interactions. Results for the S22 set of typical organic molecular dimers are promising.
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| 7. |
- Berland, Kristian, 1983, et al.
(author)
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van der Waals density functionals built upon the electron-gas tradition: Facing the challenge of competing interactions
- 2014
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 140:18, s. 18A539 -
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Journal article (peer-reviewed)abstract
- The theoretical description of sparse matter attracts much interest, in particular for those ground-state properties that can be described by density functional theory. One proposed approach, the van der Waals density functional (vdW-DF) method, rests on strong physical foundations and offers simple yet accurate and robust functionals. A very recent functional within this method called vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B89, 035412 (2014)] stands out in its attempt to use an exchange energy derived from the same plasmon-based theory from which the nonlocal correlation energy was derived. Encouraged by its good performance for solids, layered materials, and aromatic molecules, we apply it to several systems that are characterized by competing interactions. These include the ferroelectric response in PbTiO3, the adsorption of small molecules within metal-organic frameworks, the graphite/diamond phase transition, and the adsorption of an aromatic-molecule on the Ag(111) surface. Our results indicate that vdW-DF-cx is overall well suited to tackle these challenging systems. In addition to being a competitive density functional for sparse matter, the vdW-DF-cx construction presents a more robust general-purpose functional that could be applied to a range of materials problems with a variety of competing interactions.
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| 8. |
- Berland, Kristian, 1983, et al.
(author)
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van der Waals forces in density functional theory: a review of the vdW-DF method
- 2015
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In: Reports on Progress in Physics. - : IOP Publishing. - 0034-4885 .- 1361-6633. ; 78:6, s. 066501-
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Journal article (peer-reviewed)abstract
- A density functional theory (DFT) that accounts for van der Waals (vdW) interactions incondensed matter, materials physics, chemistry, and biology is reviewed. The insights that ledto the construction of the Rutgers–Chalmers van der Waals density functional (vdW-DF) arepresented with the aim of giving a historical perspective, while also emphasizing more recentefforts which have sought to improve its accuracy. In addition to technical details, we discussa range of recent applications that illustrate the necessity of including dispersion interactionsin DFT. This review highlights the value of the vdW-DF method as a general-purpose method,not only for dispersion bound systems, but also in densely packed systems where these typesof interactions are traditionally thought to be negligible.
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| 9. |
- Block, Jan, 1973, et al.
(author)
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Ultrathin Pd and Pt Films on W(211)
- 2003
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In: Thin Solid Films. ; 428, s. 47-
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Journal article (peer-reviewed)abstract
- The transition metals Pd and Pt have, in bulk, approximately the samenearest neighbor distance as tungsten, so that ultrathin Pd or Pt filmscan be grown on W substrates without creating significant strain.In the present work we studyultrathin Pd and Pt films on the atomically rough W(211) surface byfirst-principles density-functional theory (DFT) methods.Previous experiments, summarized here, have shown that in filmsthicker than 1 physical monolayer (PML), tungsten atoms of the substratediffuse into the film to create alloys. Both toconfirm the alloy formation from theory and to help characterize the alloyswe present studies of Pd and Pt films with included W atoms. The DFT resultsallow us to indicate the energetically preferred alloy structures.
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| 10. |
- Borck, O., et al.
(author)
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Methylbenzenes on graphene
- 2017
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 664, s. 162-167
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Journal article (peer-reviewed)abstract
- We present a theory study of the physisorption of the series of methylbenzenes (toluene, xylene and mesitylene), as well as benzene, on graphene. The aim is two fold: we provide data that will be used as input to larger-scale methods like molecular-dynamics simulations, and at the same time we enhance the basic understanding of graphene used as a material for sensors and as an idealized model for the carbon in active carbon filters. The molecules are studied in a number of positions and orientations relative to graphene, using density functional theory with the van der Waals functional vdW-DF. The molecules are adsorbed fractional coverage. We focus on the vdW-DF1 and vdW-DF-cx functionals, and find that the binding energy of the molecules on graphene grows linearly with the number of methyl groups, at the rate of 0.09 eV (vdW-DF1) to 0.11 eV (vdW-DF-cx) per added methyl group. We further find that the orientation of the methyl groups of the molecules relative to graphene is at least as important as the lateral position of the whole molecule on graphene. © 2017 Elsevier B.V.
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