[CP2K-user] [CP2K:19840] Cons. Qty for different ensembles + Pressure fluctuation

[Léon Luntadila Lufungula]

Dear Matthias,

My apologies, I forgot to add the input files. You can find them in 
attachment to this message.

Kind regards,
Léon

On Monday 29 January 2024 at 10:36:30 UTC+1 Léon Luntadila Lufungula wrote:

> Dear Matthias,
>
> I've also tried to equilibrate a box of 216 water molecules with DFT and 
> while the temperature and pressure seem to equilibrate quite easily, the 
> constant of motion shows large jumps despite the potential and kinetic 
> energy also being quite constant... If I'm not mistaken, the constant of 
> motion in the NPT ensemble is the energy of the system + the energy of the 
> thermostat + energy of barostat, as shown in this lecture 
> <https://www.cp2k.org/_media/events:2016_summer_school:cp2k_moving_atoms.pdf> 
> from 2016, so this would suggest that the fluctuations are due to the 
> thermostat or barostat, right? Like the TIP3P NPT run, I used a thermostat 
> timecon of 100 fs and a barostat timecon of 1000 fs and after 21 125 fs 
> (blue vertical line in figures), I restarted the calculation and increased 
> the thermostat timecon to 500 fs. I accidentaly set RESTART_BAROSTAT and 
> RESTART_BAROSTAT_THERMOSTAT to FALSE upon restarting, but I'm unsure if 
> this might have lead to the large jumps in the constant of motion later at 
> t > 28 000 fs... 
> [image: H2O-DFT-6x6x6-equilibration.png]
> Same goes for the NPT_F calculation of my solvated TiO2 slab. I did a 10 
> ps simulation with thermostat timecon 50 and barostat timecon 100 and 
> everything seems to equilibrate except for the constant of motion which 
> seems to steadily rise. After 10 ps of simulation I restarted the 
> calculation and again accidentaly messed up my input and set 
> RESTART_BAROSTAT and RESTART_BAROSTAT_THERMOSTAT to FALSE but this time I 
> didn't even change the timecons of the thermostat and barostat, but this 
> time I immediately see a significant jump in the constant of motion after 
> which it continues to increase... Any idea how I can fix this so that the 
> constant of motion stays...well...constant?
> [image: a101-solv10-NPT_F-equilibration.png]
>
> Kind regards,
> Léon
>
> On Tuesday 23 January 2024 at 14:41:46 UTC+1 Léon Luntadila Lufungula 
> wrote:
>
>> 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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