[CP2K-user] Help about AIMD equilibration time for liquid water and water interface simulation

[唐博]

I meet the same question,I asked some people who have much experience about 
cp2k,I thought the question is the TIMECON parameter under the NOSE,the 
default value is the 1000[fs],it means that the temperature exchange every 
1000fs,I set the parameter value to 100fs,it will be fine for fast 
equlibration!You can try!
tangbo USTC 
在 2019年1月11日星期五 UTC+8上午6:45:41，Shuai Jiang写道：
>
> Hi, all,
>
>  
>
> Recently I am trying to utilize AIMD in CP2K to equilibrate liquid water 
> and water clusters for further analysis. According to the literature, after 
> classical MD equilibration, 2 ps in AIMD would be long enough to 
> equilibrate the system under the NVT condition with Nose-Hoover thermostat 
> (see Fig.1. Input). But under my test, for liquid water (32 water molecules 
> composing cluster with PBC, TIP5P equilibrated), even after 5ps, the 
> temperature still changes significantly (Fig.1.). So I change the input 
> parameters (including decreasing time steps from 1fs to 0.5 fs, decreasing 
> the inner scf max cycles while increasing the outer scf cycles, changing 
> DFT from BLYP to PBE, increasing EPS_SCF from 1E-5 to 1E-6, changing 
> thermostat from Nose to GLE) with the same input configuration, it turns 
> out that the most influencing parameter for temperature equilibration is 
> thermostat (see Fig.2. for GLE results). It seems like that GLE could 
> equilibrate the liquid water faster. But why isn’t Nose-Hoover thermostat 
> working in my test? A lot of literature use Nose-Hoover thermostat for 
> equilibration and NVE for production.
>
>  
>
> For simulating SO2 interacting with small water cluster surface to test, 
> the equilibration time is much longer as the temperature oscillates 
> significantly (Fig.3.) even though it is after almost 18 ps equilibration! 
> The small water cluster is composed of 24 water molecules and equilibrated 
> under TIP3P for 1ns, then the SO2 molecule is put around it, then do the 
> geometry optimization with BLYP-D3 till convergence as the initial 
> configuration for AIMD. So I am curious about the same question as that in 
> simulating the liquid water: why Nose-Hoover thermostat cannot equilibrate 
> my system in several ps as indicated in the literature? The faster 
> equilibration under GLE thermostat rules out the issue of initial 
> configuration, so are there some parameters wrongly setting? Thanks in 
> advance.
>
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