Fix reax/c/species issue with oxide

Hi,

I am depositing 100 oxygen atoms of a silver surface. I am use fix reax/c/species to see what silver has left the surface to ultimately track erosion. However, the fix reax/c/species is considering it as one large molecule which is not making sense. The molecule contains 67 O, and the other 33 bounce off the surface. When I look at the image after deposition there is a significant growth of the iron and it really does not look bonded.

As another test I shrunk my box so that the initial silver substrate only had 12 A to expand and anything past that was considered eroded. In this I observed that over 120 silver atoms were greater than 12 A away from the original surface! I believe this is far further than what the oxide layer thickness should be yet it is still considered bonded.

Moreover, between the 0-12A there are 45 of the 67 oxygen atoms. Meaning there is only 22 left to bond with the 120 that are lost. There is no AgO combination that would make this work.

Why then is reax/c/species still considering it as one big bonded molecule?

initial silver.PNG

after impact.PNG

Hi Alex,

the fix is doing a simple thing: if the bond order (BO) of a bond between two atoms is larger than some threshold value (0.3 by default), the atoms are attributed to the same molecule. That is, “molecule” here is a set of atoms for which you can follow interatomic bonds from one atom to any other atom of the set so that each of these interatomic bonds has BO higher than 0.3. You can adjust the BO threshold using “cutoff” keyword of the fix.

That being said, it is up to you to propose criteria to distinguish atoms that have left the surface.

Regards,
Oleg

04.08.2018, 15:55, “Alex Morrissey” <lmorrissey157@…24…>: