[CP2K-user] Water-bilayer/Metal interface - Ab intio MD

Marcella Iannuzzi marci... at gmail.com
Thu Mar 21 16:00:16 UTC 2019

Dear Anna, 

which type of calculations did you carry out in preparation of the MD run?
Is your DFT model reproducing the correct lattice structure?
Did you optimise the slab and check that the electronic structure of the 
bulk and at the surface is what expected from reference data?
I do not know this specific system, but the parameters in the DFT section 
seem to be not very well tuned. Is the SCF converging? Do you get 
reasonable forces?

Did you model the adsorption of individual water molecules to evaluate the 
binding energy and compare to references? 
Should the layer of molecules be ice-like or do you want to simulate liquid 
If the coordinates are obtained from some structural data or geometry 
optimisation, did you anneal slowly from 0K to the final temperature?
Why are you running NPE? Did you already thermalised at constant volume?

Kind regards

On Thursday, March 21, 2019 at 3:55:19 PM UTC+1, Anna Anic wrote:
> Hey everybody,
> I am trying to do Ab-initio MD for a metal-water interface. I am using a 
> symmetric slab and positioned a bilayer of water at both surface sites. 
> Now, if I run the simulation my water layer just decomposes into the 
> vacuum region. That is why I would like to implement an vacuum potential 
> barrier at some point in the z-direction to prevent my water from just 
> "flying away".
> I tried using the &EXTERNAL_POTENTIAL keyword and defined a harmonic 
> function as a barrier.
> But when I run the simulation the hydrogen atoms from the H2O-bilayer  are 
> "blown away".
> The question is, what did I do wrong? Is the idea legit? Does anyone have 
> a proposal how to fix the problem or how to do it differentey.
> Greetings,
> Anna
> (I attached my input file,geometry and trajectory )
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