posted on 2012-09-11, 00:00authored byHui Li, Xiao Cheng Zeng
Motivated by a recent atomic-force-microscopy (AFM) study
of water
adlayers on mica by Heath and co-workers (Graphene Visualizes the
First Water Adlayers on Mica at Ambient Conditions. Science2010, 329, 1188), we performed an ab initio molecular dynamics study of structural and dynamic
properties of monolayer, bilayer, and trilayer water adlayers on the
muscovite mica (001) surface with and without a graphene coating.
We find that in the first epitaxial water adlayer, water molecules
that form strong hydrogen bonds with the oxygen on the mica surface
show little motions, thereby solid-like, while those “bridging”
water molecules on top of the first water adlayer exhibit “itinerant”
behavior, thereby liquid-like. Overall, the Born–Oppenheim
molecular dynamics (BOMD) simulations (based on the BLYP-D functional)
show that the first water adlayer on mica exhibits a unique hybrid
solid–liquid-like behavior with a very low diffusion coefficient
at ambient conditions. In particular, no dangling hydrogen bonds are
found in the first water adlayer on mica. Moreover, the bilayer and
trilayer water adlayers show slightly higher structural stability
than the first water adlayer. A graphene coating on the water adlayer
further enhances stability of the water adlayers. Most importantly,
the bilayer water adlayer on mica with the graphene coating becomes
fully solid-like, the structure of which is the same as the bilayer
slice of ice-Ih with
a thickness of 7.4 Å, consistent with the AFM measurement.