Problem with 'set'

Dear users,

Good Day !!
I am trying to immobilise a fraction of particles within my simulation box. Following is what I have done in input script:

# Initialization
units lj
dimension 3
boundary p p p
atom_style atomic

# Atom definitions
lattice sc 1.0
region SimBox block 0 20.0 0 20.0 0 20.0 units box
create_box 1 SimBox
create_atoms 1 random 7000 476994 NULL

mass 1 1.0
velocity all create 1.0 675957 dist gaussian

# Set a bunch of particles immobile
set group immobile type/fraction 2 0.3 12393
mass 2 1.0
velocity immobile set 0.0 0.0 0.0

Now while running I get the following : ERROR: Invalid value in set command.
‘Set’ command seems to be quite straightforward. Can someone please spare two minutes and point out my dumb mistake?

I have another question. Can I use ‘create_atoms’ twice and use ‘set’ afterwards as following:
create_atoms 1 random 6000 476994 NULL

create_atoms 2 random 1000 476994 NULL

set group immobile type 2

Thanks in advance for your time and advise.
Best regards,


I am sorry. I did not set the group-id itself prior changing it. It was gross. Sorry again for bothering you.