Dear Lammps users,
I use a Lammps version of the 6th of March 2015 and I'd like to use the fix move command that uses a dynamic group as group-input. Unfortunately, I get the error 'Fix 7 (= fix move) does not allow use of dynamic group (../modify.ccp:228). I read on the group-doc page, that not all fixes allow the use of dynamic group and I think this is the case.
My intention was to create a flow by adding a velocity to atoms in this region. Is there in Lammps a option to do this without creating the error mentioned above ?
I know there is also the option to add a force (within a region) to atoms, but if it is possible I would prefer to add velocities
I'm glad for every suggestion
Kind regards
Lisa
Fix move has an option to assign velocities, and you can also just use velocity command set keyword.
Ray
Fix move apparently can work with per-atom variables as input, so if your region is simple enough you might be able to define a boolean math function that is zero for atoms outside of the region, and you could use that with fix move. In this case though, you still have to make sure that atoms for which this variable is 0 are still integrated properly.
Is there a strong reason to prefer velocities over forces? If your system is viscous anyway (due to fix langevin or fix viscous or something) applying a force leads to the same effect, but it feels more natural to me somehow.
Dear Lammps users,
I use a Lammps version of the 6th of March 2015 and I'd like to use the
fix move command that uses a dynamic group as group-input.
Unfortunately, I get the error 'Fix 7 (= fix move) does not allow use of
dynamic group (../modify.ccp:228). I read on the group-doc page, that
not all fixes allow the use of dynamic group and I think this is the case.
My intention was to create a flow by adding a velocity to atoms in this
fix move doesn't "add" a velocity. fix move *moves* the atoms
according to some prescribed rules (from the input). that is not
adding a velocity but would be forcing atoms to move at a given
velocity.
region. Is there in Lammps a option to do this without creating the
error mentioned above ?
you would have to write your own fix.
I know there is also the option to add a force (within a region) to
atoms, but if it is possible I would prefer to add velocities
adding velocities and adding forces are essentially the same thing for
as long as the atoms have the same mass (if not, you can compensate
for it using an atom style variable, but i doubt it will have a
significant impact unless you are simulating a dilute gas).
axel.
Fix addforce can be used to induce a flow. It can be
applied to atoms in a region.
Steve