question on ion bombardment using reaxff

Hi all,

My goal is to bombard a metallic substrate with several H protons similar to an irradiation experiment. I have read a lot of posts in the message boards about this and several papers. Despite the wealth of information there still appears to be some inconsistencies.

I see several posts saying that when using reax/c you need to have the fix qeq charge equilibration. The problem with this is that it will immediately attempt to bring my system to a neutral charge, which I do not want. However when reading the manual I now see that “Using the keyword checkqeq with the value no turns off the check for fix qeq/reax, allowing a simulation to be run without charge equilibration. In this case, the static charges you assign to each atom will be used for computing the electrostatic interactions in the system. See the fix qeq/reax command for details.” If I do this will it properly simulate my charged system. Previous papers on irradiation damage say that reaxFF includes a polarizable charge function and is therefore suitable (1).

As an alternative, I also see significant mentions about electronic stopping during such simulations. One paper uses a hybrid reaxFF ZBL potential to model the interactions and electronic stopping (2). There is also mention of the fix electron/stopping command in LAMMPS, that needs the use of a ZBL potential and SRIM. The manual states this is necessary for ion bombardment. Is this a more suitable way?

Overall based on previous papers my instinct would be to define charges, turn of qeq and use reax. I am now wondering if this is correct?

Thanks for all your help!

  1. “chemical dynamic characteristic of kapton polyamide damaged by electron beam radiation” Rahnamoun 2019
  2. "Solar wind ion impacts into ice surfaces: a molecular-dynamics study

using the REAX force field" Anders 2016

  1. d by
    electron beam irradiation