[CP2K-user] [CP2K:15490] Some inconsistencies in reproducing the virial kinetic energies

am...@gmail.com amin.... at gmail.com
Tue Jun 1 08:34:45 UTC 2021

Dear Thomas,
thanks a lot for sharing that. I couldn't find eq. 23 in the provided 
paper, probably eq 20 ? 
Also, about the ener file, both the printed temperature and kinetic 
energies seem strange and I still have not been able to figure out what 
they represent exactly.
Best regards,

On Monday, May 31, 2021 at 3:27:22 PM UTC+2 tkuehne wrote:

> Dear Amin, 
> using the centroid viral estimator you compute the correct quantum kinetic 
> energy. I suspect 
> that in the ener file the classical kinetic energy or the difference to 
> the quantum kinetic energy 
> is printed. See for instance Eq. 23 of the appended paper. Also, let me 
> add that the effective 
> temperature is P*T, where P is the number of beads … 
> Best, 
> Thomas
> P.S. https://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.043305
> Am 31.05.2021 um 14:51 schrieb am... at gmail.com <am... at gmail.com>:
> As an update, I could figure it. With Eq (5) in the provided paper, the 
> virial kinetic energies and the values which CP2K would be equal if for the 
> term 3/2KT the temperature T is always almost a fixed value and equal to 
> the temperature at which the simulation is done. 
> It means there should be some bug or different meaning for the temperature 
> and kinetic energy which CP2K prints in the first three columns.
> On Sunday, May 30, 2021 at 6:21:11 PM UTC+2 am... at gmail.com wrote:
>> Hi everyone,
>> In running some path integral MD simulation in cp2k I have observed some 
>> strange issues and would be grateful if someone can comment on that.
>> After running the attached input script main.inp, the energy terms are 
>> printed in a file named “md-01-energy-1.dat”. 
>> The first issue which I encountered is that the kinetic energy printed 
>> out in the third column can no way be related to the calculated 
>> temperatures printed in the 5th column. Regardless of the degree of 
>> freedom and unit conversion factors, at least there should be a correlation 
>> between them which doesn’t exist here.
>> The second and more important issue: The calculated virial kinetic energy 
>> which is printed in the fourth column of “md-01-energy-1.dat” file also 
>> seems kind of strange. This value is calculated via the virial estimator 
>> written as equation (5) in the attached pdf file. 
>> To reproduce what CP2K prints, I manually calculated the second term in 
>> right hand side of eq (5) using the position of the centroids and beads 
>> printed out by the script and for the gradient of the potential energy 
>> required by eq(5) I also used the forces which CP2K prints. 
>> Something really surprising and unusual which I observed is that the 
>> second term in right hand side of eq (5) which I manually calculated 
>> *before* adding 3/2KT to it (as should be done based on the virial 
>> estimator) shows a perfect correlation with the total virial kinetic energy 
>> which CP2K prints (R=1.00) (although for this the virial kinetic energies 
>> which CP2K prints are ca. 438 times the values which I calculate and I 
>> couldn’t find the reason even with trying various possible unit 
>> conversions). 
>> If I also add the data I obtain with 3/2KT which should be done to yield 
>> the total kinetic energies, then the correlation coefficient dramatically 
>> reduced. 
>> I would highly appreciate your comments/helps.
>> Best regards,
>> Amin
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