[CP2K-user] [CP2K:20626] Re: Barostat/Thermostat mass units?

[Michela Benazzi]

As a followup note, I had more errors in my first email, so please 
disregard the numbers except for the main question:

The barostat mass I calculated with
N_f = 3*64 atoms
T = 1200 K
t_p = 50 fs

is W = 1.3243919e-49 kg*m2. If I normalize it dividing by the Bohr radius 
squared, W = 4.7294895e-29 kg.

Converted: W = 0.0284816321 amu or W = 51.9188808691 m_e, which is still 
nowhere close to the ~10^6 value that my RESTART file shows for the CP2K 
barostat mass. That is where I would love some suggestions. Thank you!

Michela

On Tuesday, August 27, 2024 at 12:18:25 PM UTC-4 Michela Benazzi wrote:

> * Degrees of freedom = 3*N atoms, and the units on my answer are J*s2 = 
> kg*s2. 
> Sorry about the typos. Is the number normalized by the Bohr radius^2?
> On Tuesday, August 27, 2024 at 9:06:47 AM UTC-4 Michela Benazzi wrote:
>
>> 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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