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)

5. SIMULATIONS EXPERIMENT
COMPARISON BETWEEN SIMULATION RESULTS (AVERAGED OVER 12 GLASS SURFACES) AND EXPERIMENTAL DATA
SIMULATIONS EXPERIMENT
DRY SURFACES
2 member rings (0.13/nm2) / nm2 FTIR [Bunker, 1989]
3 member rings (4.2 Si 3 memb/ nm2) Si 3 memb/ nm2 Raman [Brinker]
Si E's increase at surface ESR [Hochstrasser, 1972]
WET SURFACES
Removal of 2 memb rings / nm2 FTIR [Bunker, 1989]
Decrease in 3 memb rings (2.1 Si 3 memb/ nm2) Si 3 memb/ nm2 Raman [Brinker]
Removal of E's ESR [Hochstrasser, 1972]
Geminal sites ( ~18%) % NMR [Maciel, 1980]
Silanol concentration (3.4/ nm2 - 5/ nm2) / 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. H H H H O O O O O O O O Si Si Si Si O O O O O O O O H H H H O O O O O
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. . H in SiOH on glass O in 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) .