[lammps-users] fix langevin + fix_modify: possible bug?

Dear colleagues,
Dear Steve,

it seems to me that I found a bug connected with fix langevin and fix_modify.

It is written in the manual about the langevin fix that "the way that
temperature is computed by this fix can be changed by using the fix_modify
command". But the sample script (see below) results in the message 'ERROR:
Illegal fix_modify command'. Similar error holds for the 17Jan05 and for the
latest 12Apr06 version.

(If I change the langevin fix to the temp/rescale fix than everything works fine.)

At the same time, in the fix_modify man-page it is not written that fix_modify
can be applied to fix langevin. Where is the mistake?

Any comments will be greatly appreciated!


units lj
boundary p p p

atom_style atomic
lattice fcc 0.905

region box block 0.0 5.0 0.0 5.0 0.0 5.0
region heatedr block 0.0 5.0 0.0 5.0 0.0 2.0

create_box 1 box

create_atoms 1 box
mass 1 1.0
group heated region heatedr
temperature heated_T heated full

pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 2.5

velocity all create 0.8 5812775 mom yes rot yes dist gaussian

thermo 200

fix 1 all nve
fix 2 heated langevin 0.8 0.8 10.0 87263
#fix 2 heated temp/rescale 10 0.8 0.8 0.02 1.0
fix_modify 2 temp heated_T

timestep 0.005
run 1000

Fix langevin does not actually compute a temperature, hence
you cannot use fix_modify to set a temperature for it. I think
you must be looking at an old (incorrect) doc page for
fix langevin. The one on the WWW doesn't say you can
use fix_modify.