Fix qeq/reax with Chromium

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1

Hello LAMMPS-users,

I am working on a simulation of binary Fe-Cr alloys in the presence of an oxide film. In order to better represent the system, I am considering charge equilibration procedures to set the per-atom charges near & within the oxide layer. I am aware of the ffield.reax.Fe_O_C_H parameter set in lammps/potentials, but do not see any parameter sets containing chromium atoms from which I can determine the chi, eta, and gamma values to place in my qeq.reax parameter file.

Are there any such unpublished datasets, or would I be better-off with a blanket statement assigning fixed charges?

Otherwise, would I be able to populate the values for Cr chi, eta, and gamma from a multitude of sources? I tend to think not, but since pair potentials are largely set by other force fields, I am unsure.

Also, am I correct in assuming that chi is the Mulliken electronegativity?

Thanks for your time,
Ben

2

Maybe Aidan can answer these Qs. Although fix qeq/reax is
most commonly used with ReaxFF, you should think of it as
independent. If you are using it on your own, then those params
really have nothing to do with ReaxFF, so you could find them
in any other literature source that discusses charge equilibration.

Steve

3

Making charge assignments in isolation from other parts of the interatomic
potential is generally a bad idea. However, there are cleaver people out
there who do it, and they do meaningful calculations. I would compare it to
riding a bicycle with no hands. If you have to ask how to do it, then you
probably should not be doing it.