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Alex Granovsky
gran@classic.chem.msu.su

>I've encountered a problem during an IRC job. The problem is that starting from the saddle point (located by a Saddle plus Hessian job) and using the keyword FORWRD=.T. and FORWRD=.F. brings me to the same products.

Usually, the reasons causing the problem you have encountered are as follows:

• The imaginary frequency is rather small, and
  
• The saddle point was not located with high precision required in this situation
  

The solution to this problem is to reoptimize saddle point with tighter OPTTOL. This should be fast as you already have Hessian and geometry, and should take only few additional geometry optimization steps.

Hope this helps,
Alex Granovsky

On Jan 30 '11 1:54pm, Luca Maidich wrote
--------------------------------------------
>Good day to everyone,
>I've encountered a problem during an IRC job. The problem is that starting from the saddle point (located by a Saddle plus Hessian job) and using the keyword FORWRD=.T. and FORWRD=.F. brings me to the same products.
>After looking at my input file I realized that my mistake could be in keyword SADDLE=.F. which tells to the program that I'm at a transition state.

>A possible clue could be that imposing SADDLE=.F. the program goes in the same direction using both FORWRD=.T. and FORWRD=.F.?
>I've already searched in the manual (file input_colated.pdf) but I haven't found a confirm to my supposition.

>Any help would be greatly appreciated.
>Thanks in advance
>Luca Maidich

[ This message was edited on Mon Jan 31 '11 at 12:09pm by the author ]