[lammps-users] EAM Aluminium Potential


On my systems the potential Al_vtr.eam and Al_u9.eam are not working: All atoms are lost in less than 50 steps. But Al_jnp.eam works fine. This is my script:

******* SCRIPT *******
boundary p p p
units metal
atom_style atomic
lattice fcc 4.05
region box block 0 15 0 15 0 15
create_box 1 box
create_atoms 1 box
mass * 26.981538

pair_style eam
#pair_coeff * * Al_vtr.eam
#pair_coeff * * Al_u9.eam
pair_coeff * * Al_jnp.eam

timestep 0.002
thermo 1
fix nve all nve

minimize 1e-4 1000 1000
run 100
******* SCRIPT *******

What am I missing?

Best regards and nice weekend:

I'm having a similar problem, and found eam/alloy and NiAlH_jea.eam.alloy (previously nialhjea.eam.alloy) to work. Can anyone comment on the accuracy of using this potential file for a one component system? Are there defaults for pure Al included in this alloy system?

Gerolf -- check the SourceForge archives, I believe there was a discussion on this a month or so ago.

Mike Sellers
Grad Student, UB Chem Eng

Gerolf Ziegenhain wrote:

Thanks for the quick reply.

In the previous posting there was no real solution given. The lattice constants for the potentials are specified in their header or not? Even if the lattice constant might be slightly different: with periodic boundaries the system should not explode.

Besides the exploding the bulk modulus in dependency on the lattice constant looks very strange for the not working Al-potentials. For a given lattice constant a the bulk modulus B=V*d^2E/dV^2=-Vdp/dV at finite temperature can be obtained by just printing out the energy/pressure once without running any dynamics. B(a) should be smooth. It is smooth for the copper potentials or the mentioned working Al-potentials. But for the not-working potentials it is strange.

So what could be the problem with these potentials? I cannot find any failure in my scripts, so it seems to me, that there is a problem with the potential files.



Would you mind taking a look at this question (see below) from Gerolf
Ziegenhain about the Al_vtr.eam and Al_u9.eam potentials in LAMMPS? I
tried running these potentials here and they crashed for me too. Are
we doing something wrong (see Gerolf's input script below)? Or is it
possible that there is an error in how we've implemented these
potentials in LAMMPS?



My only addition to this thread is that I include EAM potential
files with the LAMMPS distribution when people give them
to me. So far as I know, there are no bugs in the code within
LAMMPS that runs EAM, but I can't vouch for the parameters
in the files. I do know that if an alloy file (e.g. NiAlH) was
parameterized for NiAl alloys (with H inclusions), it may not
be good to run it for pure Al.

The only solution may be to go back to the original papers
that defined these EAM potentials and look at their parameters
and test cases they ran for validation, then verify the
parameters are correct in the EAM potential files in LAMMPS
and try to run those validation problems. Unfortunately, not
all the potential files included in LAMMPS have their origins