[lammps-users] energy minimization question updated

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1

Hi Steve,

Thank you for your reply. I am still not sure how to do the energy minimization without dynamics. As you suggested, I did the example indent problem in LAMMPS, and only use minimize after each fix command. But I think the results are not correct. The minimization only has one iteration in each step, and the lattice was not affected by the indenter. So that’s why I always use run before the minimize command. The input script is like this:

2d indenter simulation

dimension 2
boundary p s p

atom_style atomic
neighbor 0.3 bin
neigh_modify delay 5

create geometry

lattice hex 0.9
region box block 0 20 0 10 -0.25 0.25
create_box 2 box
create_atoms 1

mass 1 1.0
mass 2 1.0

LJ potentials

pair_style lj/cut 2.5
pair_coeff * * 1.0 1.0 2.5

define groups

region 1 block INF INF INF 1.25 INF INF
group lower region 1
group mobile subtract all lower
set lower atom 2

initial velocities

fix 2 lower setforce 0.0 0.0 0.0

indenter

fix 4 all indent 1000.0 sphere 10 13 0 5.0
fix 5 all enforce2d

Run with indent

thermo 1

dump 1 all atom 1 tmp.dump

minimize 1.0e-4 1000 1000
fix 4 all indent 1000.0 sphere 10 12 0 5.0

dump_modify 1 every 1
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 11.8 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 11.6 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 11.4 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 11.2 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 11.0 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 10.8 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 10.6 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 10.4 0 5.0
minimize 1.0e-4 1000 1000

fix 4 all indent 1000.0 sphere 10 10.2 0 5.0
minimize 1.0e-4 1000 1000

If you think somewhere is wrong, could you give me some suggestions? Thanks a lot!

Yours,

Jie Lian

2

There were some bugs with how fix indent was used by the
minimizer. I just posted a patch (4 Aug 06) on the WWW site
that fixes the problems. Note that you do have to turn
on the fix_modify energy option with the indent fix to include
the energy of the indentation in the total PE of the system, which
is what the minimizer is working to minimize.

The script below illustrates how to set the fix and the fix_modify to
do a series of indentation steps and minimize at each stage.
Note that the last couple do not set fix_modify correctly, so the
minimizer doesn't "see" the indenter.

Steve