Diferent Temperature from ave/chunk temp and compute temp

LAMMPS LAMMPS General Discussion
1

Hi,
I’m working on a system with Silica and Water with a timestep of 2 [fs]
The silica is running with (Temp/berendsen 300 K + NVE)
"fix 1 silica nve
fix 2 silica temp/berendsen 300 300 50 "

and to compute the temperature I use
“compute Tsilica silica temp”.
To see what is happening inside the silica.
I’m using
"compute bins_temp2 all chunk/atom bin/2d y 170 1.1 z lower 1.1 compress no
fix temp_bin2 silica ave/chunk 40 50 2000 bins_temp2 temp file tempsi.data "
This simulation run for 0.3 [ns].
With the “Tsilica temp” the log shows me 300 [K], but when I analize the tempsi.data
The inside temperature of the silica it’s around of 400 [K].
Why is this difference? I suppose the Tsilica temp with 300 [K] is the correct. But why the chunks shows me another temperature.

2

There is not enough information here to make any specific statements.

The only thing I can remark is that using fix temp/berendsen is not a good way to promote equipartitioning of kinetic energy (similar for fix nvt) since it acts globally. Actually, the scaling of velocities in fix temp/berendsen somewhat emphasizes the local fluctuations of kinetic energy.