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

[am...@gmail.com]

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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