Fix ave/atom

Dear All
I am trying to calculate the dipole moment correlation function using fix/ave atom command.

The input file is given below:

dimension 3
units real
boundary p p p

kspace_style ewald 1.0e-4

kspace_modify order 3
atom_style full
pair_style lj/cut/coul/long 11.0
bond_style harmonic
angle_style harmonic
pair_modify mix arithmetic
newton off
read_data water_nvt.lammps
#read_restart xfile.restart.100000
group cat type 1
group ain type 2
group wtr type 1 2

neighbor 1.0 bin
neigh_modify delay 0 every 1 one 6000
minimize 1.0e-4 1.0e-6 100 1000
fix 1 wtr shake 0.0001 20 0 t 1 2 a 1 b 1

fix 2 all nvt temp 300.0 300.0 100.0
compute ab all rdf 200 1 1 1 2 2 2
fix 3 all ave/time 100 1 100 c_ab file rdf.out mode vector

compute bc all property/atom mux muy muz
fix 4 all ave/atom 1 100 100 mux muy muz c_bc file atom.out
timestep 0.5

thermo 1000
thermo_style custom step pe ke etotal temp press vol

restart 50000 z.restart

dump 1 all custom 10 z.output.dump id type efieldx efieldy efieldz
dump 2 all custom 10 z1.output.dump id mol type x y z
run 500000

but i get the error with the msg :compute property/atom for atom property that isn’t allocated

and if i caculate scaled positions using the same fix/ave statement it gives the error msg
:Illegal fix ave/atom command

How should i correct these errors?
I am using lammps Nov 2010 version.

DeepaK Ojha
School Of Chemistry

“Selfishness is not living as one wishes to live, it is asking others to live as one wishes to live”

Dear Deepak,

You get the “invalid compute” error because atoms of “full” style indeed don’t have such property as per-atom dipole moment.
You probaly need to create atom-style variables like

variable mux atom x*q

and use them in fix ave/atom.

Vasily Pisarev

Vasily is correct, mux is only defined if you
are using atom_style dipole. x*q is not
the same thing, i.e. it is not a point dipole
on top of an atom.