[CP2K-user] [CP2K:17233] Re: SG-CPMD/cons. Q

[Marcella Iannuzzi]

Hi,
To satisfy the equipartition theorem, every degree of freedom should  have 
the same average, 1/2KT
If the temperature is not the desired one, it is necessary to adjust the 
gamma better
It is normal that the fewer the degrees of freedom are, the larger the 
temperature's fluctuations, though the averages should be the right ones

Kind regards
Marcella


On Monday, June 27, 2022 at 2:26:00 PM UTC+2 a.celi... at gmail.com wrote:

> Dear Marcella,
> thanks for your answer!
> In my case  <Ekin> = 5.3 eV and 3/2*N*kB*T = 4.6eV,  is 0.7 eV too much 
> difference? 
> My target Temperature is 330 K, and the <T> from the calculation is 
> roughly 380 K. In the attached file the temperature of the region are 
> plotted, region of water molecules (32H2O) and region of the first layer Pt 
> atoms (12Pt). Only first layer is allowed to moved.
> What I dont get is why the region of Pt atoms is oscillating a lot?
>
> BTW energy plots are in Hartree units.
>
> Best regards,
>
>
>  
>
> El jueves, 23 de junio de 2022 a las 16:07:42 UTC+2, Marcella Iannuzzi 
> escribió:
>
>> Dear Alexandra
>>
>> If you properly selected the noisy gamma and the equipartition theorem is 
>> satisfied, the generated  Langevin dynamics should sample the canonical 
>> ensemble.
>>
>> Regards
>> Marcella
>>
>> On Tuesday, June 21, 2022 at 12:44:20 PM UTC+2 a.celi... at gmail.com wrote:
>>
>>> Dear cp2k-users,
>>> thanks to Marcell's suggestions and to Onofrio:
>>>
>>> -Always start sgcpmd from a well converged wfn obtained along a standard 
>>> BOMD run with diagonalisation and smearing
>>> -  Let the first steps run on many scf iterations if needed, i.e., set 
>>> MAX_SCF large enough
>>> -  But use a relative large eps_scf. The wfn is not going to be 
>>> optimised as in the BOMD, energy convergence  around 10^-5 is desirable
>>> - Use FULL_ALL preconditioner + ASPC
>>> - Use a small time step
>>> - Tune properly GAMMA and NOISY_GAMMA
>>>
>>> Now my calculations are converging! Thanks a lot! Per MD step roughly 5 
>>> iterations.
>>> My system is water/Pt(111),  therefore I used the GAMMA and NOISY_GAMMA 
>>> from Lan, Jinggang, Jürg Hutter, and Marcella Iannuzzi. "First-principles 
>>> simulations of an aqueous CO/Pt (111) interface." *The Journal of 
>>> Physical Chemistry C* 122.42 (2018): 24068-24076.
>>>
>>> My question is regarding the cons. Q. In ENSEMBLE NVT the cons. Q is 
>>> equal to the total energy of my system plus energy of thermostat. The 
>>> energy of the thermostat can be also printed (for only NVT ENSEMBLE) and I 
>>> was able to verify it. In ENSEMBLE LANGEVIN, which is also at constant 
>>> temperature, the cons. Q is equal to the total energy of my system. Is that 
>>> correct? 
>>> Maybe I am missing something, because I would interpret it as my system 
>>> is NVE instead of NVT. Can anybody enlighten me, please?
>>>
>>> I attached the plots of the energies (Hartree units), E_T = cons. Q - Ek 
>>> - Ep in case of Langevin and NVT ensemble. I know that is a very short 
>>> simulations but it is just for getting some understanding.
>>>
>>> Many thanks in advance,
>>> Alexandra
>>>
>>

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