| 1. |
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| 2. |
- Arpaia, Riccardo, 1985, et al.
(författare)
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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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Ingår i: Physical Review Materials. - 2475-9953. ; 3:11
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Filter function of graphene oxide: Trapping perfluorinated molecules
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 152:2
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23, s. 135001-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Harris-type van der Waals density functional scheme
- 2013
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 88:4
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Tidskriftsartikel (refereegranskat)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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| 6. |
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| 7. |
- Berland, Kristian, 1983, et al.
(författare)
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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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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 140:18, s. 18A539 -
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Tidskriftsartikel (refereegranskat)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.
(författare)
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van der Waals forces in density functional theory: a review of the vdW-DF method
- 2015
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Ingår i: Reports on Progress in Physics. - : IOP Publishing. - 0034-4885 .- 1361-6633. ; 78:6, s. 066501-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Ultrathin Pd and Pt Films on W(211)
- 2003
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Ingår i: Thin Solid Films. ; 428, s. 47-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Methylbenzenes on graphene
- 2017
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 664, s. 162-167
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Tidskriftsartikel (refereegranskat)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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| 11. |
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| 12. |
- Borck, Øyvind, 1971, et al.
(författare)
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Adsorption of Methanol on Aluminum Oxide: A Density Functional Study
- 2003
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Ingår i: ATB-Metallurgie. - 0365-7302. ; 43, s. 342-
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Konferensbidrag (refereegranskat)abstract
- Theoretical calculations based on density functional theory have made significant contributions to our understanding of metal oxides, their surfaces, and the binding of molecules at these surfaces. In this paper we investigate the binding of methanol at the alpha-Al2O3(0001) surface using first-principles density functional theory. We calculate the molecular adsorption energy of methanol to be E^g_ads=1.03 eV/molecule. Taking the methanol-methanol interaction into account, we obtain the adsorption energy E_ads=1.01 eV/molecule. Our calculations indicate that methanol adsorbs chemically by donating electron charge from the methanol oxygen to the surface aluminum. We find that the surface atomic structure changes upon adsorption, most notably the spacing between the outermost Al and O layers changes from 0.11 Angstrom to 0.33 Angstrom.
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| 13. |
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| 14. |
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| 15. |
- Borck, Øyvind, 1971, et al.
(författare)
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First-principles study of the adsorption of methanol at the alpha-Al2O3(0001) surface
- 2006
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Ingår i: J. Phys.: Condens. Matter. ; 18, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- We present density functional theory calculations of methanol molecular adsorption at the (0001) surface of alpha-Al2O3, for methanol coverages of 1/4 to 1 monolayer (ML). Adsorption energies, adsorption-induced restructuring of the surface, and induced changes to the electronic structure are calculated. We find that methanol bonds with its O atom to Al atoms at the alpha-Al2O3(0001) surface with an adsorption energy of 1.23 eV at coverage 1/4 ML, decreasing with coverage to 1.03 eV at 1 ML coverage. From calculations of the relaxed adsorption geometry and the angular dependence of the total energy, we predict an orientation of the adsorbed methanol molecule that has the molecular COH plane tilted away from the surface normal. The adsorption of methanol significantly restructures alpha-Al2O3(0001), especially for the outermost Al layer. Upon adsorption a small charge transfer from the molecule to the substrate takes place.
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| 16. |
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| 17. |
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| 18. |
- 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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| 19. |
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| 20. |
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| 21. |
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| 22. |
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| 23. |
- Cooper, V.R., et al.
(författare)
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Stacking Interactions and the Twist of DNA
- 2008
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Ingår i: Journal of the American Chemical Society. ; 130, s. 1304-
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Tidskriftsartikel (refereegranskat)abstract
- The importance of stacking interactions for the Twist and stability of DNA is investigated using the fully ab initio van der Waals density functional (vdW-DF). Our results highlight the role that binary interactions between adjacent sets of base pairs play in defining the sequence-dependent Twists observed in high-resolution experiments. Furthermore, they demonstrate that additional stability gained by the presence of thymine is due to methyl interactions with neighboring bases, thus adding to our understanding of the mechanisms that contribute to the relative stability of DNA and RNA. Our mapping of the energy required to twist each of the 10 unique base pair steps should provide valuable information for future studies of nucleic acid stability and dynamics. The method introduced will enable the nonempirical theoretical study of significantly larger pieces of DNA or DNA/amino acid complexes than previously possible.
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| 24. |
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| 25. |
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| 26. |
- Ericsson, Jonas, 1994, et al.
(författare)
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Involving High School Students in Computational Physics University Research: Theory Calculations of Toluene Adsorbed on Graphene
- 2016
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203 .- 1932-6203. ; 11:8, s. e0159168-
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Tidskriftsartikel (refereegranskat)abstract
- To increase public awareness of theoretical materials physics, a small group of high school students is invited to participate actively in a current research projects at Chalmers University of Technology. The Chalmers research group explores methods for filtrating hazardous and otherwise unwanted molecules from drinking water, for example by adsorption in active carbon filters. In this project, the students use graphene as an idealized model for active carbon, and estimate the energy of adsorption of the methylbenzene toluene on graphene with the help of the atomic-scale calculational method density functional theory. In this process the students develop an insight into applied quantum physics, a topic usually not taught at this educational level, and gain some experience with a couple of state-of-the-art calculational tools in materials research.
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| 27. |
- Frostenson, Carl Mikael, 1992, et al.
(författare)
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Hard and soft materials: Putting consistent van der Waals density functionals to work
- 2022
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Ingår i: Electronic Structure. - : IOP Publishing. - 2516-1075. ; 4:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present the idea and illustrate potential benefits of having a tool chain of closely related regular, unscreened and screened hybrid exchange-correlation (XC) functionals, all within the consistent formulation of the van derWaals density functional (vdW-DF) method (Hyldgaard et al (2020 J. Phys.: Condens. Matter 32 393001)). Use of this chain of nonempirical XC functionals allows us to map when the inclusion of truly nonlocal exchange and of truly nonlocal correlation is important. Here we begin the mapping by addressing hard and soft material challenges: Magnetic elements, perovskites, and biomolecular problems.We also predict the structure and polarization for a ferroelectric polymer. To facilitate this work and future broader explorations, we present a stress formulation for spin vdW-DF and illustrate the use of a simple stability-modeling scheme. The modeling supplements density functional theory (DFT) (with a specific XC functional) by asserting whether the finding of a soft mode (an imaginary-frequency vibrational mode, ubiquitous in perovskites and soft matter) implies an actual DFT-based prediction of a low-temperature transformation.
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| 28. |
- Hyldgaard, Per, 1964, et al.
(författare)
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Interpretation of van der Waals density functionals
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 90:7
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Tidskriftsartikel (refereegranskat)abstract
- The nonlocal correlation energy in the van der Waals density functional (vdW-DF) method can be interpreted in terms of a coupling of zero-point energies of characteristic modes of semilocal exchange-correlation (xc) holes. These xc holes reflect the internal functional in the framework of the vdW-DF method. We explore the internal xc hole components, showing that they share properties with those of the generalized-gradient approximation. We use these results to illustrate the nonlocality in the vdW-DF description and analyze the vdW-DF formulation of nonlocal correlation.
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| 29. |
- Jacobson, Niclas, 1971, et al.
(författare)
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Hydrogen dynamics in magnesium and graphite
- 2002
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Ingår i: Computational Materials Science. ; 24, s. 273-277
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium, nanotubes, graphitic nanofibers, and graphite represent interesting opportunities for efficient hydrogen storage applications and motivate first-principle investigations of the hydrogen energetics and dynamics that describe such potential technological usage. We presentspin-polarized electron-density calculations of adsorption energies and dffusion barriers for bothchemisorbed and physisorbed hydrogen atoms to provide a detailed description of the importanthydrogen dynamics.
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| 30. |
- Jiao, Yang, 1985, et al.
(författare)
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Extent of Fock-exchange mixing for a hybrid van der Waals density functional?
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 148:19
-
Tidskriftsartikel (refereegranskat)abstract
- The vdW-DF-cx0 exchange-correlation hybrid design [K. Berland et al., J. Chem. Phys. 146, 234106 (2017)] has a truly nonlocal correlation component and aims to facilitate concurrent descriptions of both covalent and non-covalent molecular interactions. The vdW-DF-cx0 design mixes a fixed ratio, a, of the Fock exchange into the consistent-exchange van der Waals density functional, vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)]. The mixing value a is sometimes taken as a semi-empirical parameter in hybrid formulations. Here, instead, we assert a plausible optimum average a value for the vdW-DF-cx0 design from a formal analysis; A new, independent determination of the mixing a is necessary since the Becke fit [A. D. Becke, J. Chem. Phys. 98, 5648 (1993)], yielding a 0 = 0.2, is restricted to semilocal correlation and does not reflect non-covalent interactions. To proceed, we adapt the so-called two-legged hybrid construction [K. Burke et al., Chem. Phys. Lett. 265, 115 (1997)] to a starting point in the vdW-DF-cx functional. For our approach, termed vdW-DF-tlh, we estimate the properties of the adiabatic-connection specification of the exact exchange-correlation functional, by combining calculations of the Fock exchange and of the coupling-constant variation in vdW-DF-cx. We find that such vdW-DF-tlh hybrid constructions yield accurate characterizations of molecular interactions (even if they lack self-consistency). The accuracy motivates trust in the vdW-DF-tlh determination of system-specific values of the Fock-exchange mixing. We find that an average value a 0 = 0.2 best characterizes the vdW-DF-tlh description of covalent and non-covalent interactions, although there exists some scatter. This finding suggests that the original Becke value, a 0 = 0.2, also represents an optimal average Fock-exchange mixing for the new, truly nonlocal-correlation hybrids. To enable self-consistent calculations, we furthermore define and test a zero-parameter hybrid functional vdW-DF-cx0p (having fixed mixing a 0 = 0.2) and document that this truly nonlocal correlation hybrid works for general molecular interactions (at reference and at relaxed geometries). It is encouraging that the vdW-DF-cx0p functional remains useful also for descriptions of some extended systems. Published by AIP Publishing.
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| 31. |
- Jiao, Yang, 1985, et al.
(författare)
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Signatures of van der Waals binding: A coupling-constant scaling analysis
- 2018
-
Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:8
-
Tidskriftsartikel (refereegranskat)abstract
- The van der Waals (vdW) density functional (vdW-DF) method [Rep. Prog. Phys. 78, 066501 (2015)RPPHAG0034-488510.1088/0034-4885/78/6/066501] describes dispersion or vdW binding by tracking the effects of an electrodynamic coupling among pairs of electrons and their associated exchange-correlation holes. This is done in a nonlocal-correlation energy term Ecnl, which permits density functional theory calculation in the Kohn-Sham scheme. However, to map the nature of vdW forces in a fully interacting materials system, it is necessary to also account for associated kinetic-correlation energy effects. Here, we present a coupling-constant scaling analysis, which permits us to compute the kinetic-correlation energy Tcnl that is specific to the vdW-DF account of nonlocal correlations. We thus provide a more complete spatially resolved analysis of the electrodynamical-coupling nature of nonlocal-correlation binding, including vdW attraction, in both covalently and noncovalently bonded systems. We find that kinetic-correlation energy effects play a significant role in the account of vdW or dispersion interactions among molecules. Furthermore, our mapping shows that the total nonlocal-correlation binding is concentrated to pockets in the sparse electron distribution located between the material fragments.
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| 32. |
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Kleis, Jesper, 1974, et al.
(författare)
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Van der Waals interaction of simple, parallel polymers
- 2005
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Ingår i: Journal of Chemical Physics. ; 122, s. 164902-
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Tidskriftsartikel (refereegranskat)abstract
- We study the mutual interactions of simple parallel polymers within the framework of density-functional theory (DFT). As the conventional implementations of DFT do not treat the long-range dispersion fvan der Waals (vdW) interactions, we develop a systematic correction scheme for the nonlocal energy contribution of the polymer interaction at the intermediate to the asymptotic separations. We primarily focus on the three polymers, polyethylene, isotactic polypropylene, and isotactic polyvinylchloride, but the scheme presented applies also more generally to other simple polymers. From first-principle calculations we extract the geometrical and electronic structures of the polymers and the local part of their interaction energy, as well as the static electric response. The dynamic electrodynamic response is modeled on the basis of these static calculations, from which the nonlocal vdW interaction of the polymers is extracted.
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| 38. |
- Kuisma, Elena, 1979, et al.
(författare)
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Graphene oxide and adsorption of chloroform: A density functional study
- 2016
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 144:18, s. Art. no. 184704-
-
Tidskriftsartikel (refereegranskat)abstract
- Chlorinated hydrocarbon compounds are of environmental concerns, since they are toxic to humans and other mammals, and are widespread, and exposure is hard to avoid. Understanding and improving methods to reduce the amount of the substances are important. We present an atomic-scale calculational study of the adsorption of chlorine-based substance chloroform (CHCl3) on graphene oxide, as a step in estimating the capacity of graphene oxide for filtering out such substances, e.g., from drinking water. The calculations are based on density functional theory, and the recently developed consistent-exchange functional for the van der Waals density-functional method is employed. We obtain values of the chloroform adsorption energy varying from roughly 0.2 to 0.4 eV per molecule. This is comparable to previously found results for chloroform adsorbed directly on clean graphene, using similar calculations. In a wet environment, like filters for drinking water, the graphene will not stay clean and will likely oxidize, and thus adsorption onto graphene oxide, rather than clean graphene, is a more relevant process to study.
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| 39. |
- Lanai, Victor, 1990, et al.
(författare)
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Differences in interaction of graphene/graphene oxide with bacterial and mammalian cell membranes
- 2023
-
Ingår i: Nanoscale. - 2040-3372 .- 2040-3364. ; 16:3, s. 1156-1166
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Tidskriftsartikel (refereegranskat)abstract
- Graphene, a single layer, hexagonally packed two-dimensional carbon sheet is an attractive candidate for diverse applications including antibacterial potential and drug delivery. One of the knowledge gaps in biomedical application of graphene is the interaction of these materials with the cells. To address this, we investigated the interaction between graphene materials (graphene and graphene oxide) and plasma membranes of cells (bacterial and mammalian cells). The interactions of four of the most abundant phospholipids in bacteria and mammalian plasma membranes with graphene materials were studied using density functional theory (DFT) at the atomic level. The calculations showed that the mammalian phospholipids have stronger bonding to each other compared to bacterial phospholipids. When the graphene/graphene oxide sheet is approaching the phospholipid pairs, the bacterial pairs exhibit less repulsive interactions, thereby a more stable system with the sheets was found. We also assembled bacterial and mammalian phospholipids into liposomes. We further observed that the bacterial liposomes and cells let the graphene flakes penetrate the membrane. The differential scanning calorimetry measurements of liposomes revealed that the bacterial liposomes have the lowest heat capacity; this strengthens the theoretical predictions of weaker interaction between the bacterial phospholipids compared to the mammalian phospholipids. We further demonstrated that graphene oxide could be internalized into the mammalian liposomes without disrupting the membrane integrity. The results suggest that the weak bonding among bacteria phospholipids and less repulsive force when graphene materials approach, result in graphene materials interacting differently with the bacteria compared to mammalian cells.
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| 40. |
- 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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| 41. |
- 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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| 42. |
- Le, Duy, et al.
(författare)
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Physisorption of nucleobases on graphene: a comparative van der Waals study
- 2012
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42, s. 424210-
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Tidskriftsartikel (refereegranskat)abstract
- The physisorption of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) on graphene is studied using several variants of the density functional theory (DFT): the generalized gradient approximation with the inclusion of van der Waals interaction (vdW) based on the TS approach (Tkatchenko and Scheffer 2009 Phys. Rev. Lett. 102 073005) and our simplified version of this approach (here called sTS), the van der Waals density functional vdW-DF (Dion et al 2004 Phys. Rev. Lett. 92 246401) and vdW-DF2 (Lee et al 2010 Phys. Rev. B 82 081101), and DFT-D2 (Grimme 2006 J. Comput. Chem. 27 1787) and DFT-D3 (Grimme et al 2010 J. Chem. Phys. 132 154104) methods. The binding energies of nucleobases on graphene are found to be in the following order: G > A > T > C > U within TS, sTS, vdW-DF, and DFT-D2, and in the following order: G > A > T ~ C > U within DFT-D3 and vdW-DF2. The binding separations are found to be different within different methods and in the following order: DFT-D2
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| 43. |
- Lee, Kyuho, et al.
(författare)
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Benchmarking van der Waals density functionals with experimental data: potential-energy curves for H2 molecules on Cu(111), (100) and (110) surfaces
- 2012
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42
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Tidskriftsartikel (refereegranskat)abstract
- Detailed physisorption data from experiment for the H2 molecule on low-index Cu surfaces challenge theory. Recently, density functional theory (DFT) has been developed to account for nonlocal correlation effects, including van der Waals (dispersion) forces. We show that the functional vdW-DF2 gives a potential-energy curve, potential-well energy levels and difference in lateral corrugation promisingly close to the results obtained by resonant elastic backscattering–diffraction experiments. The backscattering barrier is sensitive to the choice of exchange functional approximation. Further, the DFT-D3 and TS-vdW corrections to traditional DFT formulations are also benchmarked, and deviations are analyzed.
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| 44. |
- Lee, Kuyho, et al.
(författare)
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Evaluation of a density functional with account of van der Waals forces using experimental data of H2 physisorption on Cu(111)
- 2011
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Ingår i: Physical Review B. - 1098-0121. ; 84, s. 193408-
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Tidskriftsartikel (refereegranskat)abstract
- Detailed experimental data for physisorption potential-energy curves of H2 on low-indexed faces of Cu challenge theory. Recently, density-functional theory has been developed to also account for nonlocal correlation effects, including van der Waals forces. We show that one functional, denoted vdW-DF2, gives a potential-energy curve promisingly close to the experiment-derived physisorption-energy curve. The comparison also gives indications for further improvements of the functionals.
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| 45. |
- Liu, Lihui, 1985, et al.
(författare)
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A Mechanism for Highly Efficient Electrochemical Bubbling Delamination of CVD-Grown Graphene from Metal Substrates
- 2016
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Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- In most cases, transfer of chemical-vapor-deposited 2D materials from metallic foil catalysts onto a target substrate is the most necessary step for their promising fundamental studies and applications. Recently, a highly efficient and nondestructive electrochemical delamination method has been proposed as an alternative to the conventional etching transfer method, which alleviates the problem of cost and environment pollution because it eliminates the need to etch away the metals. Here, the mechanism of the electrochemical bubbling delamination process is elucidated by studying the effect of the various electrolytes on the delamination rate. A capacitor-based circuit model is proposed and confirmed by the electrochemical impedance spectroscopy results. A factor of 27 decrease in the time required for complete graphene delamination from the platinum cathodes is found when increasing the NaOH ratio in the electrolyte solution. The opposite trend is observed for delamination at the anode. The surface screening effect induced by nonreactive ions in the vicinity of the electrodes plays a key role in the delamination efficiency. The analysis is generic and can be used as a guideline to describe and design the electrochemical delamination of other 2D materials from their metal catalysts as well.
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| 46. |
- Londero, Elisa, 1982, et al.
(författare)
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Desorption of n-alkanes from graphene: a van der Waals density functional study
- 2012
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42, s. 424212-
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Tidskriftsartikel (refereegranskat)abstract
- A recent study of temperature-programmed desorption (TPD) measurements of small linear alkane molecules (n-alkanes, with formula CNH2N+2) from C(0001) deposited on Pt(111) shows a linear relationship of the desorption energy with increasing n-alkane chain length N. We here present a van der Waals density functional study of the desorption barrier energy of the ten smallest n-alkanes (of carbon chain length N = 1–10) from graphene. We find linear scaling with N, including a non-zero intercept with the energy axis, i.e. an offset at the extrapolation to N = 0. This calculated offset is quantitatively similar to the results of the TPD measurements. From further calculations of the polyethylene polymer we offer a suggestion for the origin of the offset.
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| 47. |
- Londero, Elisa, 1982, et al.
(författare)
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Role of van der Waals bonding in the layered oxide V2O5: First-principles density-functional calculations
- 2010
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 82:5, s. 054116-
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Tidskriftsartikel (refereegranskat)abstract
- Sparse matter is characterized by regions with low electron density and its understanding calls for methods to accurately calculate both the van der Waals (vdW) interactions and other bonding. Here we present a first-principles density-functional theory (DFT) study of a layered oxide (V2O5) bulk structure which shows charge voids in between the layers and we highlight the role of the vdW forces in building up material cohesion. The result of previous first-principles studies involving semilocal approximations to the exchange-correlation functional in DFT gave results in good agreement with experiments for the two in-plane lattice parameters of the unit cell but overestimated the parameter for the stacking direction. To recover the third parameter we include the nonlocal (dispersive) vdW interactions through the vdW-DF method [M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)] testing also various choices of exchange forms. We find that the transferable first-principles vdW-DF calculations stabilizes the bulk structure. The vdW-DF method gives results in fairly good agreement with experiments for all three lattice parameters.
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| 48. |
- Londero, Elisa, 1982, et al.
(författare)
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Vanadium pentoxide (V2O5): a van der Waals density functional study
- 2011
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 182:9, s. 1805-1809
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Tidskriftsartikel (refereegranskat)abstract
- The past few years have brought renewed focus on the physics behind the class of materials characterized by long-range interactions and wide regions of low electron density, sparse matter. There is now much work on developing the appropriate algorithms and codes able to correctly describe this class of materials within a parameter-free quantum physical description. In particular, van der Waals (vdW) forces play a major role in building up material cohesion in sparse matter. This work presents an application to the vanadium pentoxide (V2O5) bulk structure of two versions of the vdW-DF method, a first-principles procedure for the inclusion of vdW interactions in the context of density functional theory (DFT). In addition to showing improvement compared to traditional semilocal calculations of DFT, we discuss the choice of various exchange functionals and point out issues that may arise when treating systems with large amounts of vacuum.
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| 49. |
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| 50. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene
- 2018
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:7, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- We study the phase stability and martensitic transformation of orthorhombic and monoclimic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclimic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclimic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclimic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclimc to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.
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