Oxygen Interactions with Silica Surfaces: Coupled Cluster and Density Functional Investigation and the Development of a New ReaxFF Potential

We consider oxygen interactions with realistic silica
surfaces, including both experimentally
observed nondefective surface reconstructions and experimentally observed
surface defects. Nondefective models include clusters representing
the site above a fully coordinated surface Si atom and bridging O
atoms, and the defective models include clusters representing an under-coordinated
Si defect, a nonbridging O defect, and a ring structure. Energies
were obtained for the approach of atomic and molecular oxygen to these
clusters in various configurations by using explicitly correlated
CCSD­(T)-F12b electronic structure theory and the Minnesota density
functionals, which were found to be in good agreement. The Minnesota
functionals were employed in binding energy calculations for all of
the clusters, considering the singlet and triplet spin states for
nondefective clusters and doublet and quartet spin states for defective
clusters. We find that the chosen defects are energetically favorable
sites for binding. The density functional energies were used to extend
the empirical ReaxFFSiO potential for silica, which was
previously parametrized for bulk silica polymorphs (van Duin et al. J. Phys. Chem. A, 2003, 107, 3803–3811), to model the gas–surface interactions
represented by the defective and nondefective clusters presented here.
Interaction energy predictions from ReaxFFSiOGSI agree very well with the density functional
energies. ReaxFFSiOGSI can now be employed in reactive large-scale molecular dynamics
simulations involving oxygen–silica gas–surface interactions
such as oxide growth and the heterogeneous recombination of oxygen
occurring on real silica surfaces.