Re: Reply to "MOPAC6.0 geometry optimization"
The default minimization routine in both MOPAC 5.0 and 6.0 is BFGS. DFP
been discounted as a tremendously useful method. MOPAC 6.0 also has
eigenvector following (EF), which was not in 5.0.
Your comment concerning the necessity to check that all optimization methods
etc. are the same is salient.
I don't believe that the isomer possibility is too viable. We have done
enough tests to believe that while you do find a stationary point at higher
energy, it is typically very unrealistic as far as real chemistry (at least
for our systems).