Hi lammps-users,
I am trying to minimize by using the force criterion a system of (only) 65 Au atoms with the reax potential.
This is my input file:
%%%%%%%%%%%%%%%%%%%%%%%%%%%
REAX potential for CHO system
units real
boundary p p f
atom_style charge
read_data Au_diffusion.data
group freeze id 1:32
group unfrozen subtract all freeze
pair_style reax/c NULL
pair_coeff * * ffield.reax.AuO Au
fix 1 all qeq/reax 10 0.0 10.0 1e-6 reax/c
neighbor 2 bin
neigh_modify every 1 delay 0 check yes
thermo 1
thermo_style custom step temp pe
fix 2 freeze setforce 0.0 0.0 0.0
dump 1 all custom 1 out.trj id element type x y z fx fy fz q
min_style cg
min_modify dmax 0.01
minimize 0.0 1.0e-10 10000 100000
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
In the output file I found:
Minimization stats:
Stopping criterion = linesearch alpha is zero
The forces don’t fulfill the criteria, why? I tried another potential (eam) and it worked!
I really would like to know what I am doing wrong. I have seen that many other people had a similar problem, but their solution didn’t help me.
Thanks,
PS
I am (very) new using lammps.
2 Likes
Hi lammps-users,
I am trying to minimize by using the force criterion a system of (only) 65
Au atoms with the reax potential.
This is my input file:
*%%%%%%%%%%%%%%%%%%%%%%%%%%%*
# REAX potential for CHO system
units real
boundary p p f
atom_style charge
read_data Au_diffusion.data
group freeze id 1:32
group unfrozen subtract all freeze
pair_style reax/c NULL
pair_coeff * * ffield.reax.AuO Au
fix 1 all qeq/reax 10 0.0 10.0 1e-6 reax/c
neighbor 2 bin
neigh_modify every 1 delay 0 check yes
thermo 1
thermo_style custom step temp pe
fix 2 freeze setforce 0.0 0.0 0.0
dump 1 all custom 1 out.trj id element type x y z fx fy fz q
min_style cg
min_modify dmax 0.01
minimize 0.0 1.0e-10 10000 100000
*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*
In the output file I found:
* Minimization stats:*
* Stopping criterion = linesearch alpha is zero*
The forces don’t fulfill the criteria, why? I tried another potential
(eam) and it worked!
I really would like to know what I am doing wrong. I have seen that many
other people had a similar problem, but their solution didn’t help me.
there is nothing really wrong. these kinds of things can happen with
certain minimization algorithms. the error message effectively means, that
the minimization algorithm cannot figure out in which direction to move.
minimization algorithms are not guaranteed to always drop into the global
minimum.
for some systems, and some force fields, it can be difficult to find a
minimum. sometimes also, the force field can contribute to this by being
corrugated with "ripples" and not as smooth as others. since you are
immobilizing some atoms, you're making the situation even more complex.
here are some suggestions that can help:
- switch the minimization algorithm and then go back
- or run some MD steps and then minimize
- (slightly) randomize your coordinates and minimize again
- or -as you noted- switch the force field and then go back
all of these will do about the same thing: they will modify your positions
in some more-or-less systematic way and may help to have your system "jump"
out of where it is "trapped" on the potential hypersurface.
axel.
2 Likes