# [CP2K-user] [CP2K:15013] Re: The temperature I get is different from what I set when do massive and global thermostat.

Travis polla... at gmail.com
Sat Mar 27 05:44:03 UTC 2021

```Hi,

Yes, use the configuration from geometry optimization to start MD. Though
in your original post, the thermostat coupling constant is much greater
than the length of the trajectory you ran, whether massive or global - it's
not doing anything here. The velocities are randomized and scaled to the
target temperature by default as well so you should expect differences in
the initial temperature fluctuations. After running for some time and
reaching equilibrium, the average temperature from both thermostat settings
should be equal. The massive thermostat controls every degree of freedom so
it should get to the target temperature in fewer MD steps, making it ideal
for equilibration. You should exercise caution in using MASSIVE for a given
thermostat and coupling constant when you are interested in dynamic
properties during data collection (aka production) runs. See, J. Chem.
Theory Comput. 2013, 9, 2887−2899.

-T

On Friday, March 26, 2021 at 10:15:18 PM UTC-4 tang... at gmail.com wrote:

> Hello Julian,
>      Thanks for your suggestion. I will do geometry optimization
> immediately. However, I'm a little confused about the last sentence  in
> your reply, whether I should use the structure gotten by geometry
> optimization to run massive and global thermostat firstly and than run
> others processing? I hope i have expressed my question clearly.
>       Tangyu.
>
> Julian Heske <j... at gmail.com> 于2021年3月26日周五 下午11:03写道：
>
>> Hello,
>>
>> in order to run a MD calculation at a specific tempertare, you have to
>> equilibrate the system first to reach your target temperature. The time you
>> need to equilibrate your system is dependent on your initial configuration.
>> Since you are starting with a structure which has a very high potential
>> energy (-157,5 vs. ~ -168 a. u. of the others, see out.txt), this energy
>> remains as kinetic energy in the system and the thermostat will need a long
>> time to remove the energy from the system. You can first do a geometry
>> optimization ( CP2K_INPUT <https://manual.cp2k.org/trunk/CP2K_INPUT.html>
>> / MOTION <https://manual.cp2k.org/trunk/CP2K_INPUT/MOTION.html> / GEO_OPT
>> <https://manual.cp2k.org/trunk/CP2K_INPUT/MOTION/GEO_OPT.html> ), which
>> structure as initial configuration. However, you should then still take a
>> look at the temperature and not use the equilibration steps for your
>> analysis.
>>
>> Kind regards,
>> Julian
>> tang... at gmail.com schrieb am Freitag, 26. März 2021 um 15:16:33
>> UTC+1:
>>
>>> Dears cp2k's users,
>>>       I'm doing a vibration analysis exercise.When I did massive and
>>> global thermostat, the temperature I get is different from what I set.
>>> Could you tell me what causes this error? I would appreciate you generous
>>> help. The input and output file are listed as follow.
>>>
>> --
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