[molpro-user] CCSD(T) RHF not converging

Gerald Knizia knizia at theochem.uni-stuttgart.de
Wed Jul 29 19:54:44 BST 2009

On Tuesday 28 July 2009 10:59, Jörg Saßmannshausen wrote:
> I am new to MolPro and I am running into a problem. I want to do a CCSD(T)
> calculation of an organic molecule containing N, O, Si and F as
> heteroatoms. The structure was optimised at the MP2 level of theory.
> However, when I try to run a CCSD(T) calculation, the RHF does not converge
> after 40 steps.

Did you check if your geometry is correct? Angstrom/Bohr-conversion issues 
might be a problem. Molpro will print the geometry parameters (e.g., bond 
lengths) in both Angstroem and Bohr, and you should check if they are sound.
It is *very unlikely* that Molpro's RHF will fail to converge a reasonable 
closed-shell organic compound. I don't think I've ever seen that happening.

Some other things to consider: 

> I have tried to set it to a (rediculus) high number of 300 
> with the MAXIT keyword, but somehow that seems to be ignored.

"maxit" is not a keyword. It is either a parameter or an option. So you 
generally need to use either
Unfortunately there are still some inconsistencies, with some programs 
accepting only the first form, some only the second, and some accepting 
But just saying "maxit=100" will simply create a new variable with name 
"maxit" which you can then use in further calculations or as parameter and so 
Gerald Knizia

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