units in fix qeq/reax parameters file

Dear LAMMPS Users,

I got a doubt about units of quantities in param.qeq file from fix qeq/reax command. I tried to look at the doc page and to the mailing list but I am still confused.

First, self-Coulomb potential “eta” is the same quantity reported in the third column of Table I of Rappe and Goddard III, Journal of Physical Chemistry, 105, 3358-3363 (1991) or it should be doubled or halved?

Second, “units of this fix are hard-coded to be A, eV, and electronic charge” it is not clear for me. Is it correct to say that chi", “eta” and "gamma should be respectively in eV, eV and Ang?

Thank you very much for any suggestion.
Best regards,
Paolo

Dear LAMMPS Users,

I got a doubt about units of quantities in param.qeq file from fix qeq/reax
command. I tried to look at the doc page and to the mailing list but I am
still confused.

First, self-Coulomb potential "eta" is the same quantity reported in the
third column of Table I of Rappe and Goddard III, Journal of Physical
Chemistry, 105, 3358-3363 (1991) or it should be doubled or halved?

Eta is double the value from ffield.reax.* This is because eta in
ffield.reax.* force field files are pre-multipiled by the 1/2
prefactor.

Second, "units of this fix are hard-coded to be A, eV, and electronic
charge" it is not clear for me. Is it correct to say that "chi", "eta" and

This just means that the unit system in param.qeq is A, eV and e. It
does not mean that units of chi, eta and gamma follow this order.

Thank you for the quick answer and for the information.

Dear LAMMPS Users,

I got a doubt about units of quantities in param.qeq file from fix qeq/reax
command. I tried to look at the doc page and to the mailing list but I am
still confused.

First, self-Coulomb potential "eta" is the same quantity reported in the
third column of Table I of Rappe and Goddard III, Journal of Physical
Chemistry, 105, 3358-3363 (1991) or it should be doubled or halved?

Eta is double the value from ffield.reax.* This is because eta in
ffield.reax.* force field files are pre-multipiled by the 1/2
prefactor.

Thus, just to be clear, it actually is the same quantity.

Second, "units of this fix are hard-coded to be A, eV, and electronic
charge" it is not clear for me. Is it correct to say that "chi", "eta" and

This just means that the unit system in param.qeq is A, eV and e. It
does not mean that units of chi, eta and gamma follow this order.

Note that in the param.qeq file there is no charge at all. Thus, if I understood well, it is correct to say that quantities in the param.qeq file are in eV and Ang.
Paolo