[CP2K-user] [CP2K:17128] Re: Comparison between set initial temperature and temperature calculated from velocities

[松尾拓郎]

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.akira 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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