# Reverse energy barrier (EBR) is zero for my NEB

Hello everyone
I am studying defect formation barriers by diffusing the atom to vacancy site.I am facing a problem of 0 reverse energy barrier EBR (inicating the diffusion of atom to high energy state) for my NEB calculation (I couldn’t upload the image due to restriction from matsci).This is making my calculation unphysical, with an unoptimised MEP.
can you suggest me how to come over this problem ?
here is my input
----input—
dimension 3
boundary p p p
atom_style atomic
variable u uloop 20
atom_modify map array sort 0 0.0
#initial data

#potential
pair_style tersoff
pair_coeff * * /usr/local/Cellar/lammps/20220623/share/lammps/potentials/SiC.tersoff Si C

#initial minimization to relax whole supercell
minimize 1.0e-15 1.0e-15 1000 10000
timestep 0.001
reset_timestep 0

#define groups
region surround block -3.0 5.0 INF 10.0 INF INF units box

#group of NEB atoms
group nebatoms id 879
#set group nebatoms type 2
group nonneb subtract all nebatoms

#apply nudging among replica, fix 1,fix 2,fix3 . specify as many as u want
fix 1 nebatoms neb 2.0 parallel neigh

thermo 100

#save dump
dump 1 nebatoms atom 10 dump.neb.\$u
#dump 2 nonneb atom 10 dump.nonneb.\$u
log log.sic_555_neb_m2
#run NEB

min_style quickmin
neb 0.1 0.0 5000 2000 100 final sic_555.final

The NEB algorithm is just the algorithm and LAMMPS will execute it no matter what. If you don’t get the expected results, you need to ask yourself, if your input was suitable for that purpose. That is most often due to one of two problems: 1) the geometries are not suitable (both must be local minimums), 2) you didn’t fully understand the algorithm and thus your expectations are not correct but the result is correct for the input. Neither of those are really LAMMPS problems and can be “solved” with some change of the input file parameters.

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