[molpro-user] Instability problems

Yann P. Tambouret yannpaul at bu.edu
Thu Nov 10 01:20:56 GMT 2005

I have had a similar issue.

I can rotate the orbitals so that they are in the correct energy-ordered 
order. I use the merge program.

When I run a subsequent CI calc. with the NOEXC option, I no longer see 
the instabilities.

My concern is that the MCSCF program is  optimizing the orbitals for the 
wrong CI wavefunction(s), because as you pointed out, if the orbitals 
are not in the correct order, then the active space is not defined 

Is this actually a bug, as it seems?

Attached is a pdf file showing what I've seen. This is a 7 B2g SA MCSCF 
calc. for molecular oxygen. Point (1) shows from the start that the B1u 
orbitals are miss labeled, but this does not have a great affect on the 
surfaces, as you can see in the before (bottom) and after (top) 
reordering. Point (2) shows a case where the surfaces are greatly 
affected by a rapid adjustment in the labeling.

Any help in this area would be greatly appreciated.

Yann Tambouret
Boston University

Constantine Koukounas wrote:

>Dear Molpro list,
>When i run a CASSCF calculation the orbitals (of a particular symmetry
>block) are
>not sorted in ascending energy order that causes problems since some core
>orbitals penetrate in my active space and valence orbitals in the core
>problem of course is more severe at the CI level since wrong electrons are
>Rotation does not work.What is the generic problem for that sorting?
>Instability problems result as a natural consequence of it.
>C. Koukounas
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