I am performing relaxed scan in Gaussian (B3LYP/6-31G(d,p)). There are two small organic molecules, one of which is a radical, the other has a benzene ring.
I'm trying to understand the optimization output. Specifically, the line
Optimization completed on the basis of negligible forces. I understand that these forces are the maximum and RMS forces above.
Some examples of "negligible forces" from my output file:
Item Value Maximum Force 0.000004 RMS Force 0.000001 Maximum Displacement 0.019917 RMS Displacement 0.004747 Item Value Maximum Force 0.000002 RMS Force 0.000000 Maximum Displacement 0.002231 RMS Displacement 0.000490 Item Value Maximum Force 0.000002 RMS Force 0.000001 Maximum Displacement 0.003132 RMS Displacement 0.000805
However, some small values like
Item Value Maximum Force 0.000002 RMS Force 0.000001 Maximum Displacement 0.000666 RMS Displacement 0.000149
are followed only by
Optimization completed. So what does "negligible" mean? How small do they need to be to say they are negligible? Or is this connected to at least one
NO in convergence criterion section?
Next question, how reliable is optimization when such message pops up? If it's unreliable, what do I do about this? Would altering the initial geometry fix it when in only happens in a couple of scan steps?