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| 2. |
- Baudin, M., et al.
(författare)
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Dynamics, structure and energetics of the (111), (011) and (001) surfaces of ceria
- 2000
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 468:03-jan, s. 51-61
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations for 20-30 Angstrom thick CeO2 slabs with 2-D periodicity are presented. The three low-index surfaces investigated are(lll), (011) and (001). The simulations were performed within a constant-temperature-constant-pressure ensemble and used the shell-model to describe polarizability. All simulation runs were performed at atmospheric pressure and in the temperature range 10-1100 K. For all three surfaces at both 300 and 1100 K, we find that the surface m.s. displacements are generally larger for the oxide ions than for the cations and that the out-of-plane surface motion is usually larger than the in-plane surface motion. At room temperature, the oxygen m.s. displacements at the (Ill)surface are a factor 1.2 larger than in the bulk, a factor 1.6 for the (011) surface and approximately five times larger at the metastable (001) surface compared to the bulk. The effect of the presence of a surface on the ion dynamics [and on the structure for (011)] persists all the way to the slab centres. even for these rather thick slabs. Our simulations for the polar (001) surface demonstrate that the relative stabilities of different faces and surface terminations can change with temperature, and that it may not always be meaningful to consider one specific user-prepared termination as superior to the others.
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| 3. |
- Baudin, M., et al.
(författare)
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MD simulations of a doped ceria surface - very large surface ion motion
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 335:06-maj, s. 517-523
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Tidskriftsartikel (refereegranskat)abstract
- Mean-square displacements (MSDs) and individual-ion square-displacements (ISDs) for the different constituents in Ca-doped CeO2(0 1 1) slabs at 300 K have been studied as a function of depth from the surface. Constant pressure-constant temperature MD simulations were used. The MSDs are 2-3 times larger at the surface than in the bulk, but ISDs as large as ca. 150 times the surface MSD value were observed during short-time periods for anions next to an anion vacancy at the surface. The chemical implications of this kind of motion are important, since transient structural distortions of this magnitude will lead to large electron re-distributions.
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| 4. |
- Baudin, Micael, et al.
(författare)
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MD simulations of a doped ceria surface - very large surface ion motion
- 2001
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Ingår i: CHEMICAL PHYSICS LETTERS. - 0009-2614. ; 335:5-6, s. 517-523
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Tidskriftsartikel (refereegranskat)abstract
- Mean-square displacements (MSDs) and individual-ion square-displacements (ISDs) for the different constituents in Ca-doped CeO2(0 1 1) slabs at 300 K have been studied as a function of depth from the surface. Constant pressure-constant temperature MD simu
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| 5. |
- Baudin, M., et al.
(författare)
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Molecular dynamics simulations of an Al2O3(0001 +/-, 0-10(II))/CeO2 (011 +/-,01-1(II)) interface system
- 2001
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 401:02-jan, s. 159-164
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Tidskriftsartikel (refereegranskat)abstract
- Constant stress, constant temperature (10 K, 300 K) molecular dynamics simulations were carried out with shell-model potentials for an infinite composite ceria-alumina slab with two free surfaces [alpha -Al2O3 (0001) and CeO2(011) and their opposite counterparts]. The interface introduces considerable structural and dynamical changes, both at the slab surfaces and in the center of the slab. Structurally, both oxide surfaces become effectively oxygen-terminated and the surface structures become disordered close to the interface. Dynamically, in the region near the 'alumina surface/ceria surface/alumina-ceria interface' 3-phase junction the ionic motion is considerably enhanced. Thus, in the interface region, the ionic mean-square displacements increase 2-3 times compared to the pure slabs. Moreover, the ions at the interface participate in a new kind of motion, not present in the pure oxide slabs: large occasional, but frequently reoccurring, back-and-forth ionic motions take place with square-amplitudes as large as similar to0.70 Angstrom (2).
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| 8. |
- Wojcik, M. C., et al.
(författare)
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Structure and predicted near edge x-ray absorption fine structure spectra for the surface of liquid formamide from molecular-dynamics simulation
- 2000
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 113:8, s. 3374-3380
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Tidskriftsartikel (refereegranskat)abstract
- A modification of an existing model for formamide interactions in the liquid phase makes it possible to study the bulk liquid and its free surface at conditions near the triple point, i.e., 300 K and essentially zero pressure, by (MD) molecular-dynamics simulation. Density profiles and orientation profiles in the surface region show the depth and gradual loss of the molecular ordering in the transition from bulk vapor to the bulk liquid. Near edge x-ray absorption fine structure (NEXAFS) resonance intensity spectra are computed from the orientation profiles, so that comparison should be possible with experimental depth resolved NEXAFS spectra.
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