Warnings during simulation with ReaxFF force field

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1

Hi all,

I want to use ReaxFF force field to simulate the insertion of Li ions in Si anode. However, there are always some warnings which are:

Warning: inconsistent vdWaals-parameters Force field parameters for element X indicate shielding without inner wall, but earlier atoms indicate different vdWaals-method.
This may cause division-by-zero errors. Keeping vdWaals-setting for earlier atoms.

Is anyone can help me to point out the problems in my script?

The script file is:

#------------Initialization----------------#

clear
units real
dimension 3
boundary s p p
newton on

atom_style charge

neighbor 3.0 bin
neigh_modify every 1 delay 1

#-----------------Create Atoms-----------------#

read_data data.a-Si_1000

#----------------Variable Definition------------#

variable N equal step
variable V equal vol
variable T equal temp
variable PE equal pe
variable ETOTAL equal etotal
variable P equal press
variable Lx equal lx
variable Ly equal ly
variable Lz equal lz
variable Pxx equal pxx
variable Pyy equal pyy
variable Pzz equal pzz

#--------------Output Settings-----------------#

thermo_style custom step etotal pe vol temp press
thermo 1000
timestep 0.001

#----------------velocity setting---------------#

velocity all create 300 5812775 dist gaussian units box

#--------------Initial dimensions of simulation box--------#

variable tmpx equal "lx"
variable tmpy equal "ly"
variable tmpz equal "lz"
variable Lx equal {tmpx}** **variable Ly equal {tmpy}
variable Lz equal {tmpz}** **print "Initial Lengths, Lx = {Lx}, Ly = {Ly}, Lz = {Lz}"

dump mydump all custom 50000 a-Si_insertion.lammpstrj id type x y z

fix output all print 1000 “{N} {V} {T} {PE} {ETOTAL} {P} {Lx} {Ly} {Lz} {Pxx} {Pyy} {Pzz}” file a_Si_3.75.txt

#--------------Insert Lithium atoms + Relaxation-------------#

label forloop
variable i loop 50 #insert atoms 50 times

group alloy type 1 2

create_atoms 2 random 75 721452 NULL

group Li subtract all alloy

set group Li charge 1.0

pair_style reax/c NULL

pair_coeff * * ffield.reax Si Li

fix Qeq all qeq/reax 1 0.0 10.0 1e-6 reax/c

fix 1 all nve/limit 0.1
run 30000
unfix 1

fix 2 all nvt temp 300 300 0.05
run 50000
unfix 2

write_restart restart.Li_insert.Loop$i

next i
jump Li_insertion.in forloop

#--------------Output datafiles------------#

write_data data.a-Si_insertion_3.75
write_restart restart.a-Si_insertion_3.75

Kind regards,

MC

2

Hi all,

I want to use ReaxFF force field to simulate the insertion of Li ions in Si
anode. However, there are always some warnings which are:

Warning: inconsistent vdWaals-parameters Force field parameters for element
X indicate shielding without inner wall, but earlier atoms indicate
different vdWaals-method.
This may cause division-by-zero errors. Keeping vdWaals-setting for earlier
atoms.

Is anyone can help me to point out the problems in my script?

this warning (not error) comes from reading/parsing the ffield.reax file.

3

Hi Axel,

Thank you for your help. I am wondering how to avoid such warning, because this warning always cause termination of simulation jobs.

Kind regards,

MC

4

Hi Axel,

Thank you for your help. I am wondering how to avoid such warning, because
this warning always cause termination of simulation jobs.

where did you get your force field file from?
there are different "variants" of reaxff parameterizations. the
warning hints, that you have a mix of those.
there is no indication in the code that this warning triggers an abort.

the simulation termination has to have other reasons. but the warning
may be printed for a good reason.

5

The warning is for element X, so it can not affect your simulation with elements Si and Li. This warning can not trigger any termination.

Ray