Hi Qing,
I have done quite a few simulations with LAMMPS reax/c, but only a bit
with the stand-alone code. You can try the examples in examples/reax
dir. Make sure you are using the most recent distribution.
Immediate reaction could be due to other settings, such as timestep,
initial conditions and geometry. One quick thing to check is if you
get the same energy/pressure for the first step with LAMMPS and
stand-alone Reaxff code.
Ray