[molpro-user] Problem with CC norm

Kadir Diri kadir at visual1.chem.pitt.edu
Wed Jul 14 17:33:05 BST 2004

Hi! I had the same problem in anon calculations and the shift keyword 
worked for me. I remember I spend a lot of time though, since I tried 
shift,N where N was 1, 2, 3,  etc; sometimes I had to use 5. And the 
calculations passed many cycles before they converged successfully with 
even reduced convergence criteria. In your case it might work better, 
since my calculations were on dipole-bound anions which are actually 
sometimes a trouble even for Hartree-Fock .
This question has been asked many times, here is a short but a useful 



Matt Thompson wrote:

>On Fri, 2004-07-09 at 09:31, Stavros Kardahakis wrote:
>>Dear MOLPRO users,
>>I have some problems with CCSD(T) calculations, both RCCSD(T) and
>>UCCSD(T). In particular, many times I get the error message:
>>"Unreasonable norm. Calculation stopped" and then the job crashes. Is
>>there any way someone can bypass this bottleneck (perhaps ask for
>>another type of normalization) of the CC routine?
>I am actually getting caught by this too, so I'll double the want for an
>answer.  A search showed a previous question was answered by using
>uccsd(t);shift,1; but I can't seem to figure out what that does.
>So, since nothing's worked before, I tried it.  Unfortunately, my job
>has ~3000 sec CC steps (not counting the ~3 h to get to that point), so
>it'll be a while before I know if this worked.  I'm also trying
>uhf->multi->cc rather than uhf->cc, to see if that makes any difference.
>Any suggestions from the list?
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