"fix_modify" for "fix langevin"

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1

Dear Users,

I have a problem with understanding what exactly the fix_modify command does in one of the KAPPA example codes. The question part of the code is:

heat layers

region hot block INF INF INF INF 0 1

region cold block INF INF INF INF 10 11

compute Thot all temp/region hot

compute Tcold all temp/region cold

1st equilibration run

fix 1 all nvt temp $t $t 0.5

thermo 100

run 1000

velocity all scale $t

unfix 1

2nd equilibration run

fix 1 all nve

fix hot all langevin {thi} {thi} 1.0 59804 tally yes

fix cold all langevin {tlo} {tlo} 1.0 287859 tally yes

fix_modify hot temp Thot

fix_modify cold temp Tcold

I can not understand what exactly the fix_modify commands do in the last two lines. Could you please explain me about that?

Sincerely,

Ali

2

It modifies parameters of a fix. See http://lammps.sandia.gov/doc/fix_modify.html for more details.

Ray

3

Thank you Ray, I have read that pages. My question is, what is the default method for the fix and how does it changes the parameter. I think my problem is the way fix command works. Could you explain more?

Best,
Ali

4

I believe answers to your first two questions are still in that doc page.

The way fix langevin works is explained in its doc page and accompanied papers.

Ray

5

I believe answers to your first two questions are still in that doc page.

or the documentation to fix langevin. this determined how temperature
adjustments are applied. in this case, you need to have two
thermalized regions and particles can move freely between them.

axel.

6

Thank you very much Ray and Axel. It takes some time to understand the commands and Get started with LAMMPS. Thank you for your help.

Ali