[CP2K-user] DFTB simulations of liquid water

[Guillaume Stirnemann]

Hi all, 

I am trying to simulate a box of liquid water using DFTB with periodic 
boundary conditions. My initial configuration is taken from a previous 
classical MD run performed in the NVT ensemble at the experimental density. 
I have tried different set-ups, including SCC-DFTB ("DFTB2") and 
DFTB3-diag, both with or without Grimme's D3 corrections, all ran in the 
NVT ensemble for 50 ps. 
In all cases, the simulations run well, but I end-up with a large hole in 
the simulation box. When comparing my radial distribution functions that of 
Cui who used DFBT+ (JPCB 115, 6790 (2011)), the first peak of the O-H rdf 
is usually a bit more pronounced but the contraction of the whole system is 
more visible on the second hydration shell. The differences are less 
visible for the O-O rdfs. The hole occupies about 1/2 of the simulation 
box, so the final density of my liquid phase is about 2! 

I attach the initial configuration, and the cp2k input file for DFTB2 with 
no D3. I tried on two different machines, one with 6.1 and the other one 
with 5.1. 

I am not an expert of CP2K so there might be some issues with my input, and 
your help would be very much appreciated. 

Best wishes

Guillaume 
CNRS Institut de Biologie Physico-Chimique, Paris, France





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