[lammps-users] fix heat

Dear all

I am using fix heat to generate hot wall and cold wall and expecting to get temperature gradient of my liquid in the walls. I did get it. But I found an interesting issue here:

I run my case from 10ns to 40ns, the average temperature of my hot wall is 110K, cold wall is 90K. I get a 20K temperature difference.

But I keep running my case from 20 ns to 50ns, the average temperature of my hot wall is increasing to be112K, cold wall is 92K. I get the same temperature difference.

As I keep running, the temperature of the system is increasing, but temperature difference keeps the same as my heat flux is fixed.

I am using NVE ensemble, the energy of the system should be unchanged.

I am very confused about this. On the other hand, I use fix langevin as Steve suggested before, I can get the same temperature difference without energy increasing.

So I am wondering why fix heat will cause problem like that? Or it’s me that made some mistakes.

ziyuan shi

Are you sure the energy is conserved? It's not uncommon to have some energy drift over long times.
Matt

Quoting shiziyuan <[email protected]...>: