the MD simulation of confined water and graphene

[egbertchang]

Dear All

I am trying to Run the simultion of graphene and confined water with CP2K7.1,  however I found the bulk water density is very unstable?  Can anyone look at this input file and tell me the reason? 

[Matt W]

That's what I'd expect to see from a short simulation. Try running a classical version in your favourite software. You'll need 10s of ps minimum to get sensible statistics on the water density.

[egbertchang]

but i RUN 30PS and take tha last 10PS to  Analysis . 

[Thomas Kühne]

The qualitative trend looks reasonable. Regarding the large fluctuations I was wondering 

if you are also averaging over the full length of your graphene layer and not just over a 

small slice and over time. Wrt to the latter, 10 ps is a good start, but still on the lower end. 

Best, 

Thomas Kühne

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==============================

Thomas D. Kühne

Dynamics of Condensed Matter

Chair of Theoretical Chemistry

University of Paderborn

Warburger Str. 100

D-33098 Paderborn

Germany

tdku...@mail.upb.de

+49/(0)5251/60-5726

[egbertchang]

however , in many researches, the authors take the same RUN time (10PS)t to  analysis , their figure is soomth and stable , IS 10PS TOO short to get the perfect curve ? 

[Matt W]

There is also the bin size when calculating the averages. Using a bigger bin will smooth the data over a larger volume (but you can lose resolution) are the results you quote using a similar averaging procedure to you?

Personally, I'd be surprised if you get nice data from 10ps, but I'm not doing this everyday anymore.