Illegal fix reax/c/species command

Hi lammps user,
In reaxff simulation, when using CHO force field, it is possible to use fix reax/c/species, but when I replace it with CHO_Ar force field, I get the “Illegal fix reax/c/species command” error

Without a more specific, minimal example input that allows to reproduce the issue, and information about the LAMMPS version and platform you are running on, there is very little that can be done to help you.

Thank you for your reply.The software version is 29oct2020. This is my input file,

units real

atom_style charge

pair_style reax/c lmp_control safezone 2.0 mincap 100
pair_coeff * * newffield.reax.CHO_Ar C H O
fix q all qeq/reax 1 0.0 10.0 1e-6 reax/c
neighbor 2 bin
neigh_modify every 10 delay 0 check no

minimize 1e-8 1e-8 10000 10000
reset_timestep 0

region density_calculate block INF INF INF INF 19 221
group density_calc region density_calculate

compute midu density_calc chunk/atom bin/1d z lower 0.1 units reduced
fix 1 density_calc ave/chunk 1000 10 50000 midu density/mass norm sample file density.txt

velocity all create 300 989898

fix 2 all nvt temp 300 300 10.0
fix 5 all reax/c/species 2 5 1000 temp_300K.out element C H O

thermo 1000
thermo_style custom step press pe temp ke
timestep 0.1
run 500000

unfix 2
unfix 5

fix 3 all nvt temp 300 2500 10.0
dump 4 all custom 1000 dump.50iC8H18_20nm_0.128g_temp_up id type x y z
fix 6 all reax/c/species 2 5 1000 temp_300_2500K.out element C H O
thermo 1000
thermo_style custom step press pe temp ke
timestep 0.1
run 440000

The data file used in this simulation has no argon atoms, the force field used is ffield.CHO_Ar, and then an Illegal fix reax/c/species command error occurs. When I use Ffield.CHO, no errors occur

Please note that there has been a new LAMMPS release recently. Please have a closer look at the working and not working inputs. There must be a difference in the fix reaxff/species command. This input will fail for any force field file due to a bug that was fixed recently. Please also note that this use of the fix will change your neighborlist update settings to be done only every 1000 steps which is likely to cause problems due to missed interactions.

I’ll try the new version of lammps. Thank you anyway for your valuable suggestion