problem with region command

LAMMPS LAMMPS Mailing List Mirror
1

Dear alll
I am simulating a CuZr crystal and relaxed it in such a way that I could get a lattice parameter. I started with 3.8 and relaxed the box and arrive at 4.1695 lattice parameter.

Now when i run and minimize with original dimensions(0 to 28 in x direction)it gets over in a few steps . However if i just increase the x direction by a decimal fraction my minimization continues for full 10000 steps.

What seems to be happening I cant understand. Infact now i am not even sure which is a correct crystal and which is not.

Thanks for any help

the input file is as follows

units metal
dimension 3
atom_style atomic
boundary p p p
neighbor 2.0 bin
neigh_modify delay 10 every 1 check yes exclude none page 100000 one 2000

lattice fcc 4.1695 origin 0 0 0 orient x 1 1 0 orient y -1 1 0
region simbox block 0.0 28.1 -14 14 -20 20

create_box 2 simbox
create_atoms 2 box
set group all type 1
set group all type/fraction 2 0.5 486

Define interactions

pair_style eam/fs
pair_coeff * * CuZr_mm.eam.fs Cu Zr
thermo 1
thermo_style custom step temp etotal pe press vol lx ly lz

dump ans all custom 100 crystal.lammpstrj mass id type x y z

fix relax all box/relax iso 0.0
minimize 1.0e-6 1.0e-6 10000 10000

regards,

Ashish

2

Aidan may be able to comment. There are lots of things
that can go wrong when minimizing with fix box/relax.

Steve

3

As the crystal is compressed and or expanded, bonds are turned on or turned off. Even if the resultant changes in energy are very small, they may produce multiple local minima in the energy-volume curve. From a physical point of view, shallow local minima are not significant, but LAMMPS will register them as distinct metastable crystal structures. In practice, you can deal with this by first scanning the range of physically reasonable lattice vectors to find an approximate global minimum, and then use LAMMPS minimization to refine the global minimum.