| 1. |
- Broqvist, Peter, et al.
(författare)
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ReaxFF Force-Field for Ceria Bulk, Surfaces, and Nanoparticles
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:24, s. 13598-13609
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a reactive force-field of the ReaxFF type for stoichiometric ceria (CeO2) and partially reduced ceria (CeO2-x). We describe the parametrization procedure and provide results validating the parameters in terms of their ability to accurately describe the oxygen chemistry of the bulk, extended surfaces, surface steps, and nanoparticles of the material. By comparison with our reference electronic structure method (PBE+U), we find that the stoichiometric bulk and surface systems are well reproduced in terms of bulk modulus, lattice parameters, and surface energies. For the surfaces, step energies on the (111) surface are also well described. Upon reduction, the force-field is able to capture the bulk and surface vacancy formation energies (E-vac), and in particular, it reproduces the E-vac variation with depth from the (110) and (111) surfaces. The force-field is also able to capture the energy hierarchy of differently shaped stoichiometric nanoparticles (tetrahedra, octahedra, and cubes), and of partially reduced octahedra. For these reasons, we believe that this force-field provides a significant addition to the method repertoire available for simulating redox properties at ceria surfaces.
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| 2. |
- Davis, Sergio, et al.
(författare)
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High-pressure melting curve of hydrogen
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129, s. 194508-
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Tidskriftsartikel (refereegranskat)abstract
- The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.
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| 3. |
- Davis, Sergio, et al.
(författare)
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Molecular dynamics simulation of zirconia melting
- 2010
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Ingår i: Central European Journal of Physics. - : Walter de Gruyter GmbH. - 1895-1082 .- 1644-3608. ; 8:5, s. 789-797
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Tidskriftsartikel (refereegranskat)abstract
- The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.
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| 4. |
- Kim, Sung-Yup, et al.
(författare)
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Development of a ReaxFF Reactive Force Field for Titanium Dioxide/Water Systems
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:25, s. 7838-7846
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Tidskriftsartikel (refereegranskat)abstract
- A new ReaxFF reactive force field has been developed to describe reactions in the Ti-O-H system. The ReaxFF force field parameters have been fitted to a quantum mechanical (QM) training set containing structures and energies related to bond dissociation energies, angle and dihedral distortions, and reactions between water and titanium dioxide, as well as experimental crystal structures, heats of formation, and bulk modulus data. Model configurations for the training set were based on DFT calculations on molecular clusters and periodic systems (both bulk crystals and surfaces). ReaxFF reproduces accurately the QM training set for structures and energetics of small clusters. ReaxFF also describes the relative energetics for rutile, brookite, and anatase. The results of ReaxFF match reasonably well with those of QM for water binding energies, surface energies, and H2O dissociation energy barriers. description, we have compared its performance against DFT/MD simulations for 1 and 3 monolayers of water interacting with a rutile (110) surface. We found agreement within a 10% error between the DFT/MD and ReaxFF water dissociation levels for both coverages.
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| 5. |
- Raymand, David, et al.
(författare)
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A reactive force field (ReaxFF) for zinc oxide
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 602:5, s. 1020-1031
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a reactive force field (FF) within the ReaxFF framework, for use in molecular dynamics (MD) simulations to investigate structures and reaction dynamics for ZnO catalysts. The force field parameters were fitted to a training set of data points (energies, geometries, charges) derived from quantum-mechanical (QM) calculations. The data points were chosen to give adequate descriptions of (the equations of state for) a number of zinc metal and zinc oxide phases, a number of low-index ZnO surfaces and gas-phase zinc hydroxide clusters. Special emphasis was put on obtaining a good surface description. We have applied the force field to the calculation of atomic vibrational mean square amplitudes for bulk wurtzite–ZnO at 20 K, 300 K and 600 K and we find good agreement with experimental values from the literature. The force field was also applied in a study of the surface growth mechanism for the wurtzite(0 0 0 1) surface. We find that the growth behavior depends on the presence of surface steps.
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| 6. |
- Raymand, David, 1981-, et al.
(författare)
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Hydroxylation Structure and Proton Transfer Reactivity at the Zinc Oxide-Water Interface
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 115:17, s. 8573-8579
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Tidskriftsartikel (refereegranskat)abstract
- The hydroxylation structural features of the first adsorption layer and its connection to proton transfer reactivity has been studied for the ZnO–liquid water interface at room temperature. Molecular Dynamics simulations employing the ReaxFF forcefield were performed for water on seven ZnO surfaces with varying step concentration. At higher water coverage a higher level of hydroxylation was found, in agreement with previous experimental results. We have also calculated the free energy barrier for transferring a proton to the surface, showing that stepped surfaces stabilizes the hydroxylated state and decreases the water dissociation barrier. On highly stepped surfaces the barrier is only 2 kJ/mol or smaller. Outside the first adsorption layer no dissociation events were observed during almost 100 ns of simulation time; this indicates that these reactions are much more likely if catalysed by the metal oxide surface. Also, when exposed to a vacuum, the less stepped surfaces stabilizes adsorption beyond monolayer coverage.
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| 7. |
- Raymand, David, et al.
(författare)
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Water adsorption beyond monolayer coverage on ZnO surfaces and nanoclusters
- 2008
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Ingår i: SOLAR HYDROGEN AND NANOTECHNOLOGY III. - : SPIE. - 9780819472649 ; , s. E440-E440
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Konferensbidrag (refereegranskat)abstract
- The surface structures of ZnO surfaces and ZnO nanoparticles, with and without water, were studied with a ReaxFF reactive force field (FF) and molecular dynamics (MD) simulations. The force field parameters were fitted to a training set of data points (energies, geometries, charges) derived from quantum-mechanical DFT/B3LYP calculations. The ReaxFF model predicts structures and reactions paths at a fraction of the computational cost of the quantum-mechanical calculations and as such allows dynamical simulations of reactive process for large (>>1000 atoms) and long (> 100 ps) timescales. Our simulations give the following results for the (10 (1) over bar0) surface. (i) The alternating H-bond pattern of Meyer et al. for a single monolayer coverage is reproduced by our simulations. This pattern is maintained at elevated temperatures (COOK). (ii) At coverages beyond one water monolayer we observe enhanced ZnO hydroxylation at the expense of ZnO hydration. (iii) This is achieved through an entirely new H-bond pattern mediated via the water molecules in the second layer above the ZnO surface. (iv) During a water desorption simulation at T=300K we observe that the desorption rate slows significantly when two monolayers remain. (v) Simulations of nanoparticles in the presence and absence of water suggest that water plays a key role in the determination of nanoparticle shape by catalyzing surface reconstruction reactions and stabilizing specific surface structures.
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| 8. |
- Raymand, David, 1981-, et al.
(författare)
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Water adsorption on stepped ZnO surfaces from MD simulation
- 2010
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Ingår i: Surface Science. - : Elsevier B.V.. - 0039-6028 .- 1879-2758. ; 604:9-10, s. 741-752
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a ReaxFF reactive force-field for use in molecular dynamics simulations of the ZnO–water system. The force-field parameters were fitted to a data-set of energies, geometries and charges derived from quantum-mechanical B3LYP calculations. The presented ReaxFF model provides a good fit to the QM reference data for the ZnO–water system that was present in the data-set. The force-field has been used to study how water is adsorbed, molecularly or dissociatively, at monolayer coverage on flat and stepped ZnO surfaces, at three different temperatures (10 K, 300 K, and 600 K). The stepped surfaces were created by introducing steps along the (0 0 0 1)-direction on the -surface. Equilibrium between molecular and dissociated water was observed on the terraces, resulting in a half dissociated, half molecular water monolayer. The equilibrium between dissociated and molecular water on the surface was found to be reached quickly (<10 ps). When water molecules desorb and the coverage falls, the 1:1 water–hydroxyl ratio is maintained on terraces, while steps remain largely hydroxylated. The results show that structures that promote hydrogen bonding are favored and that the presence of steps promotes an increased level of hydroxylation in the water monolayers.
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| 9. |
- van Duin, Adri, et al.
(författare)
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Development and validation of a ReaxFF reactive force field for Cu-cation/water interactions and copper metal/metal oxide/metal hydroxide condensed phases
- 2010
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:35, s. 9507-9514
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Tidskriftsartikel (refereegranskat)abstract
- To enable large-scale reactive dynamic simulations of copper oxide/water and copper ion/water interactions we have extended the ReaxFF reactive force field framework to Cu/O/H interactions. To this end, we employed a multistage force field development strategy, where the initial training set (containing metal/metal oxide/metal hydroxide condensed phase data and [Cu(H2O)(n)](2+) cluster structures and energies) is augmented by single-point quantum mechanices (QM) energies from [Cu(H2O)](2+) clusters abstracted from a ReaxFF molecular dynamics simulation. This provides a convenient strategy to both enrich the training set and to validate the final force field. To further validate the force field description we performed molecular dynamics simulations on Cu2+/water systems. We found good agreement between our results and earlier experimental and QM-based molecular dynamics work for the average Cu/water coordination, Jahn-Teller distortion, and inversion in [Cu(H2O)(6)](2+) clusters and first- and second-shell O-Cu-O angular distributions, indicating that this force field gives a satisfactory description of the Cu-cation/water interactions. We believe that this force field provides a computationally convenient method for studying the solution and surface chemistry of metal cations and metal oxides and, as such, has applications for studying protein/metal cation complexes, pH-dependent crystal growth/dissolution, and surface catalysis.
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