nve increasing temperature after nvt

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1

Dear LAMMPS Users,

I am trying to run a very basic simulation and have encountered a problem with nvt and nve. When I apply a fix nve after an nvt the temperature of the system increases.

More specifically I am simulating a thin solid film of 32800 atoms. I have fixed the bottom most atomic layer on the z-axis (800 atoms):

fix f fixed setforce 0.0 0.0 0.0

The I use the command

fix NVT mobile nvt temp 300.00 300.00 0.04 tchain 4 tloop 50

where mobile corresponds to the atoms that have not been fixed. I then unfix nvt and apply a fix nve for 2 ns.

The problem I encounter is that the temperature rises about 10-20 K when I apply a fix nve.

Does anyone have any input or suggestions?

Thank you,

Tara

2

What group was fix nve applied to, all or mobile? How did you estimate the temperature?

Ray

3

Thank you so much for getting back to me. I applied fix nve to the mobile atoms and I used the command “compute Tmobile mobile temp” to compute the temperature of the mobile atoms. I’ve included my script below.

Note I have other atomic groups as I later want to create a hot and cold junction.

Thanks again,

Tara

4

Tara,

10-20 K increase in temperature seemed fine to me. Your timestep size is already small, so I would recommend you to also minimize the volume of the supercell by adding fix box/relax. You might be able to reduce the temperature increase a bit.

Ray