I used the pair_style “reaxff”, fix_style “qeq/reaxff” and ffield “CHOFeAlNiCuSCr_v3.ff” to simulate the iron oxide (Fe2O3). However, when the simulation run, the charges of Fe and O are +0.6 and -0.4. The relative value is correct but the absolute value is wrong. Is this phenomenon normal or something goes wrong?
What do you mean by this?
According to common sense, the charge in Fe2O3 are +3(Fe) and O(-2)? I’m not sure.
These are “formal” charges for an {\rm Fe}^{3+} and an {\rm O}^{2-} ion, but these charges are usually only achieved in isolation. What you get in force field calculations are “effective” charges, which is a measure for how much atoms are polarized. Specifically for multivalent ions, the formal charge is to some degree distributed across neighboring atoms.
I get it. Thank you!