Dear LAMMPS-users (and Aidan in particular!),
I'm trying to do some simulations of cubic / tetragonal ZrO2 using the
reaxFF potential, but LAMMPS crashes after 10 fs with the message
Too many bonds on atom. Increase MBONDDEF.
I've tried various tricks to stablize it, and in the best case have
managed to reach 10 ps, but inevitably LAMMPS crashes with the same
error message.
The mailing list suggests the following possible errors, but none of
them solve the problem:
- Unphysical configuration: I've simulated this configuration (cubic or
tetragonal unit cell of ZrO2) with a Buckingham potential and get
sensible answers.
- Minimize the unit cell: I've tried "minimize" for 200 iterations
before starting NVT, but sooner or later I get the same error message
- Reduce the number of atoms per processor: The simulation cell is 3x3x3
unit cells, each of which contains 12 atoms, and I've tried both 1 and 8
processors.
- Remove the drag term from NVT and NPT: The system crashes in either
case. Incidentally, I'm using LAMMPS downloaded on 23 March 2010, before
NVT chains were added, but surely this shouldn't be so critical?
As a desparate attempt I increased the lattice parameters by 50% (which
is unphysical) and performed NVT for 875 fs followed by NPT for 875 fs.
Things looked quite stable, but then the simulation crashed with the
same error message.
Below is my input script. At the beginning of the simulation the
temperature tends to rise dramatically (to 9000 K), so I suppress the
fluctuations using temp/rescale. (I know it's not advisable to do this
together with NVT, but it's certainly not the cause of the above error
message.) The force field parameters are taken from Adri C.T. van Duin
et al., J. Phys. Chem. A 112, 139 (2008), by simply copying the
Supplementary Information into a text file. The timestep of 0.035 fs was
recommended by these authors in a subsequent paper, from which I also
took the initial charges of O and Zr.
I'd be very grateful for any suggestions,
Thanks,
Philip
boundary p p p
units real
atom_style charge
lattice custom 6 a1 1.0 0.0 0.0 a2 0.0 1.0 0.0 a3 0.0 0.0 1.01 &
origin 0.0 0.0 0.0 basis 0.0 0.0 0.0 basis 0.5 0.5 0.0
basis 0.5 0.0 0.5 basis 0.0 0.5 0.5 &
basis 0.25 0.25 0.25 basis 0.75 0.25 0.25 basis 0.25 0.75
0.25 basis 0.75 0.75 0.25 basis 0.25 0.25 0.75 basis 0.75 0.25 0.75
basis 0.25 0.75 0.75 basis 0.75 0.75 0.75
region mybox block 0 3 0 3 0 3
create_box 2 mybox
create_atoms 2 box basis 1 2 basis 2 2 basis 3 2 basis 4 2 &
basis 5 1 basis 6 1 basis 7 1 basis 8 1 &
basis 9 1 basis 10 1 basis 11 1 basis 12 1
group O type 1
group Zr type 2
set group O charge -1
set group Zr charge 2
mass 1 16
mass 2 91.22
neigh_modify one 20000 page 200000
timestep 0.035
pair_style reax 15 1.0e-6
pair_coeff * * ffield.reax 3 5
thermo_style custom step temp press pxx pyy pzz pe etotal evdwl ecoul
lx ly lz
thermo_modify flush yes
thermo 10
velocity all create 2000 891286 mom yes rot yes dist Gaussian
fix RESCALE all temp/rescale 1 2000 200070 1
fix NVT all nvt 2000 2000 0.35
run 25000
unfix NVT
unfix RESCALE
fix NPT all npt 2000 2000 0.35 aniso 0.0 0.0 0.0 0.0 0.0 0.0
10
run 25000
unfix NPT