[molpro-user] Problem regarding IRC with method QSDPATH

Ramon Hernandez ramon at uaem.mx
Wed Aug 21 16:48:57 BST 2013

Dear Mahi,

I suggest you double-check that indeed your initial CASSCF calculation
to a transition state, perhaps run a frequency calculation with tight
parameters. Then
when you run the IRC make sure you indeed converge to the same energy
as the original
CASSCF calculation. If you are sure about both these points then the
problem might really
have to do with a bug in IRC.

Also if you run again the initial frequency calculation you can save
that information and
then read it directly in the next IRC job so you avoid calculating it twice.



2013/8/21, G Mahesh <gmahesh at students.iiserpune.ac.in>:
> Dear all,
> I am familiar with MOLPRO from last two months. Since then I am trying to
> find a transition state for the reaction of reactants and products having
> multi reference character so, I am using CASSCF method for my problem.
> After a long struggle, I have found the transition state with one imaginary
> frequency (150 cm-1) and this normal mode having imaginary frequency seems
> like reaction mode which will connect reactants to products.
> Now the problem is with IRC, here, I started IRC with the geometry which I
> got from the transition state optimization with QSDPATH method and IDIR=1
> then, after Hessian calculation, it's complaining that, the given structure
> is not stationary with 4 negative Hessian eigenvalues. Does this means, my
> initial structure is not real transition state structure.....??  Should I
> have to try for the transition state structure again ..?? Any ideas to
> solve the problem....?? Pls help me...!
> Below additional details may be required to understand the problem.
> We are using the MOLPRO version 2012.
> Our system has 5 atoms. We are using 13 active orbitals and 15 active
> electrons as my cas space and AVTZ as basis.
> Thanks,
> Mahi

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