1 / 8

Multibody Potentials

We have developed a multibody potential that we have used in a large number of molecular dynamics computer simulations of glasses and interfaces. The following figures give the potential function and a few figures regarding simulations of molecules and surfaces. Multibody Potentials.

veata
Télécharger la présentation

Multibody Potentials

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. We have developed a multibody potential that we have used in a large number of molecular dynamics computer simulations of glasses and interfaces. The following figures give the potential function and a few figures regarding simulations of molecules and surfaces.

  2. Multibody Potentials Two-Body Term Three-Body Term Tetrahedral Tetra + Octahedral "Empirical Three-Body Potential for Vitreous Silica", B. P. Feuston and S. H. Garofalini, J. Chem. Phys., 89 (1988) 5818 (note error in Table I, where beta headings are mixed) "The Structure of Sodium Trisilicate Glass Via a Molecular Dynamics Simulation Employing Multibody Potentials", R. G. Newell, B. P. Feuston, and S. H. Garofalini, J. Materials Research, 4 (1989) 434. "Oligomerization in Silica Sols", B. P. Feuston and S. H. Garofalini, J. Phys. Chem. 94 (1990) 5352. "Molecular Dynamics Simulations of a-alumina and g-alumina Surfaces", S. Blonski and S. H. Garofalini, Surf. Sci. 295 (1993) 263. (check Prof. Gaorfalini’s resume for more listings of applications of the potential)

  3. MULTIBODY POTENTIAL USED TO SIMULATE MOLECULES SILICIC ACID AND POLYMERIZATION SiO2 SURFACES SILICATE GLASSES AND SURFACES FRACTURE STRENGTHS OF SILICA LEACHING OF MULTICOMPONENT GLASSES CRYSTALS

  4. FROM MOLECULAR POLYMERIZATION SIMULATIONS: SILOXANE BOND FORMATION OBSERVED IN THE SIMULATIONS • "Molecular Simulations of the Polymerization of Silicic Acid Molecules and Network Formation", S. H. Garofalini and G. Martin, J. Phys. Chem. 98 (1994) 1311. • "Sol-Gel Polymerization: Analysis of Molecular Mechanisms and the Effect of Hydrogen", G. Martin and S. H. Garofalini, J. Non-Cryst. Sol. 171 (1994) 68-79.

  5. COMPARISON BETWEEN SIMULATION RESULTS (AVERAGED OVER 12 GLASS SURFACES) AND EXPERIMENTAL DATA SIMULATIONS EXPERIMENT DRY SURFACES 2 member rings (0.13/nm2) 0.13/ nm2 FTIR [Bunker, 1989] 3 member rings (4.2 Si 3 memb/ nm2) 4.5 Si 3 memb/ nm2 Raman [Brinker] Si E's increase at surface ESR [Hochstrasser, 1972] WET SURFACES Removal of 2 memb rings 0.04/ nm2 FTIR [Bunker, 1989] Decrease in 3 memb rings (2.1 Si 3 memb/ nm2) 2.2 Si 3 memb/ nm2 Raman [Brinker] Removal of E's ESR [Hochstrasser, 1972] Geminal sites ( ~18%) 15 - 20% NMR [Maciel, 1980] Silanol concentration (3.4/ nm2 - 5/ nm2) 2 - 6/ nm2 IR [Iler, 1979; Zhuravlev, 1987]. • "Water Induced Relaxation of the Vitreous Silica Surface", B. P. Feuston and S. H. Garofalini, • J. Appl. Phys. 68 (1990) 4830.

  6. BOTH BOND FORMATION H H H H O O O O O O O O Si Si Si Si O O O O O O O O AND BOND RUPTURE H H H H O O O O O O O O Si Si O Si Si O O O O O O O ARE OBSERVED IN THE SIMULATIONS

  7. SNAPSHOT OF AN AMORPHOUS SILICA SURFACE: OXYGEN IONS SHOWN IN GREY ARE ENLARGED IN SIZE IN ORDER TO ENHANCE HEIGHT DIFFERENCES, SHOWING THE ROUGHNESS OF THE SURFACE ON THE ATOMISTIC SCALE

  8. O in glass H in SiOH on glass H2O molecules physisorbed (hydrogen bonded) onto surface sites SNAPSHOT OF AN AMORPHOUS SILICA SURFACE AFTER EXPOSURE TO WATER MOLECULES: ION SIZES ARE ENLARGED FOR THE FIGURE. WATER MOLECULES REACT AND FORM SIL.ANOLS (SiOH), WHILE SOME PHYSISORB ONTO THESE SILANOL SITES AND CLUSTER TOGETHER. SILANOL CONCENTRATION IN THIS FIGURE IS ~5/nm2. (periodic boundary conditions in plane of page) .

More Related