Problem with ReaxFF


Please send to the LAMMPS mailing list not to me, thanks.

Dear Dr. Ray,

I have a problem to run this calculation (Urea) with LAMMPS


variable f index Urea_NVT

units real

atom_style charge

boundary p p p

neighbor 2.5 bin

neigh_modify every 10 delay 0 check no

# read restart from geometry optimization

read_restart Urea.rst

pair_style reax 6.0 1 0 0.0000001

pair_coeff * * ffield.reax 1 2 3 4

I recommend you use reax/c that is faster and more flexible and reliable.

group mobile union all

velocity mobile create 800 1330944125 mom yes rot yes dist gaussian

timestep 0.01

A time step size of 0.01 fs is somewhat too small.

fix 1 mobile nvt temp 500 500 50

Your tdamp constant should be approximately 100 times the time step size.

fix rffbonds all reax/bonds 100 $f.bonds

dump 1 all atom 100 $f.dump

dump_modify 1 scale no image yes

compute reax1 all pair reax

thermo_style custom etotal ke pe temp

thermo_modify line multi

thermo 10

thermo_modify flush yes

restart 1 $f_a.rst $f_b.rst

run 100000

write_restart $f.rst

I want to run this calculation at 500K, but when I look the output file with MAPS (attached) I think that I’m not at this temperature and in fact the reactions that offers have not sense.

How can fix Temperature?

fix 1 mobile nvt temp 500 500 50 is not correct?

Change your damping factor and if it does not help, then you might have bad dynamics from bad force field and/or bad structure.

Field.reax correctly describes nitrogen?

We don’t know which force field description you are using…