boundary p p p
dimension 3
region total block -10 10 -10 10 -10 10

create_box 1 total

create_atoms 1 single 2 0 0
create_atoms 1 single 0 2 0
create_atoms 1 single 0 0 2
mass 1 1.0
pair_style zero 1.0
pair_coeff * *


fix prop all property/atom mol ghost yes
variable cluster atom ((id-1)/2)+1
fix step all nve

#run 0 # If commented out, get a segfault
set atom * mol v_cluster

dump traj all custom 1 test.dump id mol type x y z
run 1