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

[Gerald Knizia]

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: 
http://www.molpro.net/pipermail/molpro-user/2008-January/002379.html

> 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
  {progname,maxit=100}
or
  {progname;maxit,100}
Unfortunately there are still some inconsistencies, with some programs 
accepting only the first form, some only the second, and some accepting 
both...
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 
on.
-- 
Gerald Knizia