About fix append/atoms command

Dear Lammps Users

Hi

In the Lammps user guide for fix append/atoms has been written that the temp keyword will cause a region from zhi to be thermostated.

There are misunderstandings about this keyword:

Will the thermostated region expand with expanding the simulation box or the thermostated region is just a region with distance of extent argument from the current zhi?

And why we can’t use normal Nose-Hoover or Langevin thermostat for this region?

And if we want the created atoms with fix append/atom have specific initial temperature, how could we attain this?

Thanks very much

Richard J Ford

Dear Lammps Users

Hi

In the Lammps user guide for fix append/atoms has been written that the temp
keyword will cause a region from zhi to be thermostated.

There are misunderstandings about this keyword:

Will the thermostated region expand with expanding the simulation box or the
thermostated region is just a region with distance of extent argument from
the current zhi?

the documentation is very clear about this. there is a langevin
thermostat applied on the atoms between zhi and zhi-extent

And why we can’t use normal Nose-Hoover or Langevin thermostat for this
region?

because appending atoms from a regular (or randomized) lattice will
add an unwanted (small) shockwave to your system at every append
event.

And if we want the created atoms with fix append/atom have specific initial
temperature, how could we attain this?

the temp keyword does exactly that.

as i told you before. fix append/atoms is designed for a specific purpose.

axel.

Dear Axel
Hi

Thanks for your quick reply.
There is two issues yet:

In the documentation, one of the arguments for temp keyword is target. And
the target is the target velocity for region immediately ahead of piston.
1-You said that the thermostat applied on atoms between zhi-extent and zhi
and we know that the piston is in zlo. Thus the thermostated region is not
immediately ahead of piston.
2-We want to have appended atoms with specific initial temperature but temp
keyword takes initial velocity. Should we change temperature to velocity?

Am I wrong?

Sorry for taking your time
Richard J Ford

Dear Axel
Hi

Thanks for your quick reply.
There is two issues yet:

In the documentation, one of the arguments for temp keyword is target. And
the target is the target velocity for region immediately ahead of piston.
1-You said that the thermostat applied on atoms between zhi-extent and zhi
and we know that the piston is in zlo. Thus the thermostated region is not
immediately ahead of piston.

why should it? the purpose is to smoothly extend the system. nothing
else and for that it has to be exactly where it is.

2-We want to have appended atoms with specific initial temperature but temp
keyword takes initial velocity. Should we change temperature to velocity?

that is an obvious typo. have a look at the source code.

axel.

I changed the doc page to read:

target = target temperature for region immediately ahead of the piston (temperature units)

Steve