Abstract
Two different terminations of the (1010) surface
of quartz (R and β) interacting with water are simulated by
classical (CMD) (using two different force fields) and ab initio
molecular dynamics (AIMD) and compared with previously
published X-ray reflectivity (XR) experiments. Radial distribution
functions between hydroxyl and water show good agreement
between AIMD and CMDusing the ClayFF force field for
both terminations. The Lopes et al. (Lopes, P. E. M.; Murashov,
V.; Tazi, M.; Demchuk, E.; MacKerell, A. D. J. Phys. Chem. B
2006, 110, 27822792) force field (LFF), however, underestimates
the extent of hydroxylwater hydrogen bonding. The β termination is found to contain hydroxylhydroxyl hydrogen
bonds; the quartz surface hydroxyl hydrogens and oxygens that hydrogen bond with each other exhibit greatly reduced hydrogen
bonding to water. Conversely, the hydroxyl hydrogen and oxygens that are not hydrogen bonded to other surface hydroxyls but are
connected to those that are show a considerable amount of hydrogen bonding to water. The electron density distribution of an
annealed surface of quartz (1010) obtained by XR is in qualitative agreement with electron densities calculated byCMDand AIMD.
In all simulation methods, the interfacial water peak appears farther from the surface than observed by XR. Agreement among
AIMD, LFF, and XR is observed for the relaxation of the near-surface atoms; however, ClayFF shows a larger discrepancy. Overall,
results show that for both terminations of (1010), LFF treats the near-surface structure more accurately whereas ClayFF treats the
interfacial water structure more accurately. It is shown that the number of hydroxyl and water hydrogen bonds to the bridging
SiOSi oxygens connecting the surface silica groups to the rest of the crystal is much greater for the R than the β termination. It is
suggested that this may play a role in the greater resistance to dissolution of the β termination than that of the R termination.