Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations - Fuel Cell Catalysis: A Surface Science Approach - page 74

Figure 3.13 A pure H 2 O (a, b) and a mixed H 2 O/OH (c, d) hexagonal structure on Pt(111),
top view and side view.
better estimates than individual points on the viewgraph, since in this case the solvent
reduces the scatter.
The advantages of the simple approach outlined above are the limited number of
water molecules needed in the simulation and the well-defined water structure. The
major drawback is that, owing to the periodicity, this water structure fits best on a
(111) or (111)-like surface, e.g., (211). There are at least two other approximations
to model the water interaction. One is to include a large number of water molecules
and apply molecular dynamics to determine a structure for the water and include
this water arrangement in the simulations [Filhol and Neurock, 2006]. The drawbacks
of this approach are the computational time required and the results' sensitivity to the
water structure.
Another, more semiempirical, method is to assume that the only effect of the cat-
alyst is to change the binding to the surface; entropy and solvation effects are taken to
be the same as for the solvated spices. This assumes that the hydrogen bonds to, e.g.,
OH 2 are the same as the hydrogen bonding to OH [Roques and Anderson, 2004]. We