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

Gerald Knizia knizia at theochem.uni-stuttgart.de
Wed Jul 29 21:07:18 BST 2009

On Wednesday 29 July 2009 21:32, Jörg Saßmannshausen wrote:
>> Did you check if your geometry is correct?
> I have a converged geometry at the mp2/6-31g* level of theory with no
> imaginary frequencies. So I would consider that as 'correct'.

This is an issue of molecule input (wrong units, missing atoms, wrong format, 
wrong number of electrons/occupations etc). A formally "correct" geometry 
won't help you if the bond lengths are off by a factor of two due to unit 
conversion errors.

> I was using the cartesian coordinates as supplied by Molden. So I would
> have thought it is ok.

You should explicitly check it. It's printed at the start of the output.

> By the way, it finally converged with 125 steps.

If RHF requires 125 iterations for a well-behaved closed-shell molecule, then 
something is wrong. And I'd bet that it's not the RHF program.
Gerald Knizia

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