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Vinsamlegast notið þetta auðkenni þegar þið vitnið til verksins eða tengið í það: http://hdl.handle.net/1946/7680


Theoretical calculations of electrochemical systems

September 2008

We present a method of manipulating electrons in a metal slab to simulate an
electrochemical cell using an applied voltage in planewave DFT calculations. Periodic
boundary conditions are used to simulate an infinite crystal slab. By setting
the top and bottom layer of a slab at different potentials, electrons are pushed
from one side to the other; creating two oppositely charged surfaces. This effect
depends on the electric field that is produced in the vacuum between periodic
cells. We compare this method to applying a saw tooth potential, previously
used by others, and discover that our method gives a better description of the
electron transfer.
We also briefly discuss the development of our method to include a potential
profile similar to the electrical double layer near the metal surface. With our
method we get the right features of the potential profile when electrons have
been transferred to the surface, while the sow tooth potential gives exactly the
opposite direction of the potential profile with regards to the electron transfer.
We believe this could be a useful method when calculating adsorption energies of
different species as a function of bias.
We also discuss the usage of a potential energy surface based on the single center
multipole expansion in a QM/MM context with DFT calculations. This opens
the possibility of using DFT calculations for the active region at the interface,
while the bulk water phase is described with the less computationally demanding
potential energy surface.


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