[CP2K-user] [CP2K:20624] Barostat/Thermostat mass units?

[Michela Benazzi]

Hello CP2K users,
I have previously asked a question about what kind of barostat CP2K uses, 
and Thomas Kuhne linked a paper on MTTK barostat which was very helpful 
(https://aiichironakano.github.io/phys516/Martyna-Integrator-MolPhys96.pdf).

However, I tried to calculate my barostat mass to understand the units and 
I am still at a loss - currently, my restart BAROSTAT MASS is 
3.1175614526535734E+006. According to the CP2K manual, the units could be 
kg, m_e or amu. I tried to calculate it myself following the MTTK formula 
and there is no match:

W = (N_f + 9)* (k_b*T)/2 * (t_p/2pi)^2

where t_p is the time constant (50 fs), T = 1200 K and N_f is degrees of 
freedom (aka number of atoms? 64 in my system).

My result is 6.0124759e-47 J (kg*m2), which is in units of moment of 
inertia. Even if I convert it to m_e or amu it does not match:
6.0124759e-47 J (kg*m2) 

(or 3.61328477e+27 amu*m2)

(or 6.60031109024e-17 m_e*m2)


I was wondering if:


1) there are other units I have not considered in CP2K, or if CP2K 
internally converts to something else.

2) Degrees of freedom =/= number of atoms?

3) I am supposed to get rid of the m2 term by dividing by area in some way, 
although I am not sure how scientifically sound it would be, since we have 
a 3D unit cell.


Thank you very much!

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