[CP2K-user] [CP2K:17130] Re: Comparison between set initial temperature and temperature calculated from velocities

[Marcella Iannuzzi]

What about the translational and rotational degrees of freedom?
Kind regards
Marcella

On Saturday, June 11, 2022 at 4:59:33 AM UTC+2 mto wrote:

> Hi Marcella,
>
> Thank you for your response.
>
> Yes, I believe I have.
> I calculated the temperature of the system by using the following method.
>
>    1. Temperatures of each atom at 0th step were calculated with 
>    1/2*m*v^2 = 3/2*kb*T, here the value of 'm' is mass in atomic mass units 
>    (amu).
>    mass: 28.0855 (Si), 15.9994 (O), 12.0107 (C)
>    amu = 1.660538782E-27 kg
>    mSi = amu*28.0855 kg, mO = amu*15.9994 kg, mC = amu*12.0107 kg
>    v^2 = (vx^2 + vy^2 + vz^2)*10^10 (m/s)^2
>    kb = 1.3806504E-23 m^2*kg*s^-2*K^-1
>    2. 0th step temperature (T_all) is calculated 
>    I have 32 Si, 64 O and 4 C, so I calculated the temperature of each 
>    individual atom and determined the average T
>    T_Si_k = mSi*v^2/(3*kb)
>    T_O_k =  mO*v^2/(3*kb)
>    T_C_k =  mC*v^2/(3*kb) (k represents the ID of the atom.)
>    T_all = (T_Si_1 + T_Si_2 + ... +T_Si_32 + T_O_1 + T_O_2 + ... + 
>    T_O_64 + T_C_1 + T_C_2 + ... T_C_4) / (32 + 64 + 4)
>
> Is this what you were referring to when you suggested looking at the 
> degrees of freedom?
>
> Regards
> Matsuo
>
> 2022年6月10日(金) 1:04 Marcella Iannuzzi <marci... at gmail.com>:
>
>>
>> Hi 
>>
>> Are you sure that you considered the correct number of degrees of freedom?
>> Regards
>> Marcella
>>
>>
>> On Thursday, June 9, 2022 at 6:09:06 AM UTC+2 mto wrote:
>>
>>> Dear cp2k users,
>>>
>>> I wanted to conduct a comparison and performed ab initio molecular 
>>> dynamics (MD) simulations with an imposed initial temperature of 300 K. I 
>>> then calculated the temperature from the velocities at the 0th step, but 
>>> this value was 297K, which does not match with the temperature I set. I 
>>> calculated the latter temperature (297K) from '0step_velocities.xyz' 
>>> which is attached on this message. Both of them must be the same because 
>>> the 0th step velocities are determined by the initial temperature. (The 
>>> equation I used: 1/2m*v^2 = 3/2kb*T )
>>> Does anyone know why there is a difference in temperatures? 
>>>
>>> Thank you in advance,
>>> Matsuo
>>>
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