[CP2K-user] [CP2K:19803] Cons. Qty for different ensembles + Pressure fluctuation

[Léon Luntadila Lufungula]

Dear Matthias,

My AIMD calculations are on a slab wherein I keep my bottom layer fixed, 
but apparently REGION MASSIVE is not compatible with constraints, so I'll 
have to use REGION GLOBAL. Either way, thanks a lot for the detailed 
answer! For a novice MD practicioner as myself this is already enough 
information to get started! I'll try the values you suggested during my 
production run while keeping an eye on the temperature and pressure during 
the simulation; I guess when I've chosen my TIMECON too large, this will 
result in the system drifting away from the equilibrium values.

As always, thanks a lot for all the help!

Kind regards,
Léon

On Tuesday 23 January 2024 at 14:21:05 UTC+1 Krack Matthias wrote:

> Dear Léon
>
>  
>
> Using a MASSIVE CSVR thermostat with a small TIMECON of about 50 is 
> appropriate and efficient for equilibration. Thereafter, the TIMECON for 
> the thermostat can be increased to 500-1000 for the sampling (production) 
> runs and also a GLOBAL instead of a MASSIVE thermostat can be used, if 
> possible, to reduce the impact of the thermostat on the dynamics. You will 
> find different opinions about the absolute and relative values for the 
> TIMECONs of thermostat and barostat in the web or literature. I suggest to 
> use a two to five times larger TIMECON for the barostat compared to the 
> thermostat. You have, however, to keep in mind that the appropriate (best) 
> parameters for baro- and thermostat depend on the type of system and the 
> selected conditions eventually.
>
>  
>
> HTH
>
>  
>
> Matthias  
>
>  
>
> *From: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Léon 
> Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
> *Date: *Tuesday, 23 January 2024 at 11:47
> *To: *cp2k <cp... at googlegroups.com>
> *Subject: *Re: [CP2K:19801] Cons. Qty for different ensembles + Pressure 
> fluctuation
>
> Hi Matthias,
>
>  
>
> So I started an NpT directly from the inputs you gave me with a box 
> containing 216 water molecules. After a 300ps equilibration (plots thus 
> starrt at 0.3 ns), the pressure fluctuations are again in the 10kbar range 
> which is okay as you pointed out, while the average pressure is around -14 
> bar, so tha'ts also within the 20 bar range you mentioned. The energy drift 
> per atom is also below 1K so everything seems to work reasonably. 
>
>  
>
>
> I'm starting my AIMD simulations as we speak, so hopefully all goes well 
> there too. I read that it is best to do a short equilibration with a strong 
> coupling to the thermostat (e.g. CSVR, TIMECON 20 and REGION MASSIVE), 
> before going to a weaker coupling (e.g. CSVR, TIMECON 200 and REGION 
> GLOBAL), but is there also a rule of thumb w.r.t. the barostat TIMECON? I 
> regularly see TIMECON 1000, but is it useful to set it to TIMECON 100 in 
> this early equilibration?
>
>  
>
> Thanks for all the help already, it really helps me a lot given the fact 
> that I don't have a senior researcher with a lot of hands-on CP2K 
> experience around!
>
>  
>
> Kind regards,
>
> Léon
>
>  
>

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