[gpaw-users] water adsorption at various metals

[Vladislav Ivanistsev]

By trying to calculate a single water molecule adsorption at Pt slab, I
could not get a desirable value of approximately -0.3 eV, which comes from
works of Michaelides, Blanco et al, Meng etc.
For different set of parameters (k points, grid spacing, unit cell size)
I've got positive values of adsorption energy calculated in a usual way per
water molecule: Eads = Etot - Ewater - Eslab. Dipole correction and
application of vdW functional have not helped. In attached Fig. 1 are shown
results for calculations at slab. The best result has been achieved for
3*3*1 k-points for 4*4*2 Pt slab. The lowest energy is +0.1 eV. Reference
energy for water molecule used equals to -14,0 eV for default GPAW mode,
and -13,0 for lcao mode with dzp basis set.
In Fig. 2 and Fig. 3 are shown results for calculations on slab and
cluster. This time potential energy curves has been calculated, i.e. energy
at distance of 1 nm is chooses as a reference. Firstly, very small systems
shows desirable result. However, a bit bigger systems like Pt10 are
totally disappointing. Mark, that in Fig. 3 the values are close to zero.
Also information on unit size, calculation mode and cluster size is given
in legend.
Similar behavior is seen for Bi and Au surfaces, which were tested. This
points me to the fact, that I'm somewhere just wrong. Unfortunately, I
don't know where.
Please correct me and point where I might be wrong.

Gratefully,
MSc Vladislav Ivanistsev
University of Tartu, Estonia
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