Using Gaussian I've found a TS using wb97xd/3-21+g (set to opt=tight). The Freq gives me a single imaginary number. I've very happy with this. Unfortunately, when I move it up to a wb97xd/6-31+g* (with OR without the earlier force constants) the calculation fails. I get:
Item Value Threshold Converged?
Maximum Force ******** 0.000450 NO
RMS Force ******** 0.000300 NO
Maximum Displacement 0.000000 0.001800 YES
RMS Displacement 0.000000 0.001200 YES
Predicted change in Energy=-8.453459D-12
Optimization aborted.
-- No acceptable step.
I have also tried reducing the algorithm stepsize, to no success.
Any ideas?
Dear Anthony,
It is not surprising since when you upgrade or downgrade a method you actually change a lot. It might be the TS in the first method is an imaginery structure in the other.
I suggest to take the structure calculated by wb97xd/6-31+g* and do a reaction coordinate which covers the right and left side of the distance around the TS. By doing this you will locate the TS in wb97xd/6-31+g*.
Good luck,
Rafik
It looks like gaussian is stuck in a geometry it can't really make and reasonable move from. The ******** notation means that the Force was actually so large, gaussian could't nor print it in the output - that means a force of more than 99999999 (8 digitis), which calls for trouble in the optmization process.
It looks like the 3-21+G TS guess is completely off, and you should start from a different geometry.
Yes, I think you are completely correct.
For this particular TS I'm starting over again. Thanks for the answer.
Just as a quick side note, this "printing asterisks" thing is actually a peculiarity of the Fortran language, not Gaussian itself. You may get that in other software as well, but it's always the same problem - the number that is to be displayed is too large for the fixed-digit output format that has been assigned when writing the code. May either be a telltale sign of trouble in the calculations (as in your case), or a careless programmer who didn't foresee the numbers to be larger than X. Needless to say, it can break interfacing code and be a bit annoying.
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