Lower taper radius

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1

Dear lammps-users,

I am relaxing a geometry that has been relaxed with DFT. Thus, I don’t expect it to change much. However, when I run Reaxff style with 0 lower taper radius

fix 2 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c

The geometry changes a lot and the bond distances are not correct. I tried to increase the lower taper radius to 1 and see what would happen and now the geometry converges in 2 steps and doesn’t change much.

I am not sure about the definition of the lower taper radius and what it means physically but I get a warning that it is non zero. So, I am not sure whether it is OK to keep it at 1. Can someone explain what it means please?

Regards,

2

If no one here replies, I suggest you contact the ReaxFF developers.

Steve

3

Hi Steve,

I replied earlier but it hasn’t showed up.

The taper function is just mimicking long range Ewald summation that is used in charge equilibration and it should have negligible effects on dynamics (unless the equilibrium charges change significantly). It is not advised to change the taper function cutoff.

Ray