We present a study of a fa
mily of 40 unique hydroxylated
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-cristobalite surfaces generated by cleaving the
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-cristobalite unit cell along crystallographic planes to include a co
mbination of several low Miller indexsurfaces. The surface silicon ato
ms are quantified as percentages of Q
2 and Q
3 centers based on their poly
mericstate. We find that Q
3 centers are, on average, three ti
mes
more abundant than Q
2 centers. To study thesurface properties, we use two different e
mpirical potential energy functions: the
multibody potential proposedby Fueston and Garofalini (
J. Phys. Chem. 1990,
94, 5351) and the newly developed CHARMM potential byLopes et al. (
J. Phys. Chem. B 2006,
110, 2782). Our results for the surface water interactions are in goodagree
ment with previous ab initio theoretical studies by Yang et al. (
Phys. Rev. B 2006,
73, 146102) for the(100) surface. We find that the
most co
mmonly studied fa
mily of {100} surfaces is unique and is the onlysurface with 100% abundance of Q
2 centers, whereas there are nine exa
mples of surfaces with 100% Q
3centers. The predo
minantly pure Q
3 surfaces show no hydrogen bonding with the neighboring surface hydroxylgroups and weakly adsorb water overlayers. This is
markedly different fro
m the {100} pure Q
2 surface thatshows strong hydrogen bonding within the surface groups and with water. As co
mpared to all the surfacesstudied in this work, we find that the {100} surfaces are not true representations of the overall
![](/i<font color=)
mages/gifchars/beta2.gif" BORDER=0 ALIGN="
middle">-cristobalitesurfaces and their properties. We find that the two
main factors that characterize the physical properties ofsilica surfaces are the poly
meric state of the silicon ato
m and surface topography. Two types of pure Q
3crystallographic planes have been identified and are labeled as Q
3A and Q
3B based on the differences in theirtopological features. Using the {111} and {011} surfaces as exa
mples, we show that the Q
3A surface adsorbsH
2O that for
ms a stable
monolayer, but the Q
3B surface fails to for
m a stable H
2O overlayer. Othercrystallographic planes with different ratios of Q
2 to Q
3 centers are contrasted by the differences in the hydrogen-bonding network and their ability to for
m ordered H
2O overlayers.