# [lammps-users] help for fix_modify energy command

Dear all,
I’ m a new learner of lammps. I want to compute the energy from thermostat by using fix_modify energy yes, command.
But, I am not sure am I clearly understand the manual of the command. So, I express here

#--------------heat bath with the nose hoover thermostat----
fix hot f1 nvt 200.0 200.0 0.01
fix cold f10 nvt 10.0 10.0 0.01
fix_modify hot energy yes
fix_modify cold energy yes
thermo_style custom step f_hot f_cold

I am usint the nose-hoover thermostat, and dump out the energy from the thermostat by usint fix_modify and thermo_style command.

But, I found that the energy from the hot thermostat is larger than the -cold one.

Do the command, fix_modify can out put the energy from thermostat added to the system?
Do I using it in the right format?

Until now, I can’t find the clues to handle the problem.

–Thanks

Nwei

If you're applying 2 thermostats to 2 different sets of atoms,
why would you expect each of them to add/subtract the
same amount of energy to the system?

Steve

I am using the same set of atom.
At one end, nose-hoover was used to heating the system.
A the other end, nose-hoover used to cooling the system, which is the non-equilibrium system.
When time is long enough, the temperature at each layer is invariable.
At that time, the energy added from nose-hoover in heat end should be equal to the cooling one.

Another question is, if i want out dump out the energy add/subtract into the system.

fix hot f1 nvt 200.0 200.0 0.01
fix cold f10 nvt 10.0 10.0 0.01
fix_modify hot energy yes
fix_modify cold energy yes
thermo_style custom step f_hot f_cold

Am i using the right format?

2009/9/29 Steve Plimpton <[email protected]>

You don't need the fix_modify commands to look
at the f_hot and f_cold quantities in the output. But
you do need it to sum those values to the total
energy. So I would also output etotal and see if that