I modify the input like this:
[...]
*What is the right syntax?*
http://lammps.sandia.gov/doc/create_atoms.html
[...]
#create atom
create_atoms 1 region zone1 mol ar 644563 units box
[...]
and now I obtain
ERROR: Invalid atom type in create_atoms mol command
(../create_atoms.cpp:217)
Last command: create_atoms 1 region zone1 mol ar 644563 units boxbut I difine only 'type 1', how it's possible??
because you didn't pay sufficient attention to the documentation!!!
you are creating atoms as type 2 atoms (1+1 = 2!), but you (correctly)
allow only 1 atom type in your system.
axel.