[molpro-user] CASSCF energies using FROZEN

[Lorenzo Lodi]

I think I understand what was going on in my calculations, I was 
misinterpreting my inputs.

I'll explain my mistake, in case it might be useful for other people.
A line such as
CLOSED, 2; FROZEN,0;
will create CSF where the two lowest orbitals are restricted to be 
doubly occupied, but the orbitals themselves are variationally optimized.
On the other hand a line like
CLOSED, 0; FROZEN,2;
will impose no restriction on the CSF occupancy (hence producing a large 
active space than in the previous case) but will not optimize the two 
lowest orbitals.
As the active space is larger it is quite possible that the total energy 
will be lower than in the previous case.
What I really wanted to do was
CLOSED, 2; FROZEN,0;
where the active space is the same as in case 1 but the two lowest 
orbitals are not optimized. The total energy will then be higher than in 
case 1, as expected.

Lorenzo


Il 12/04/2013 18:30, Lorenzo Lodi ha scritto:
> Hello,
> I have noticed that in some cases I get lower CASSCF energies when using
> FROZEN orbitals than when specifying the same orbitals by CLOSED. I
> would like to know if this is caused by convergence to a local minimum
> of the CLOSED calculation or if this situation is somehow 'correct'.
> Naively, I would expect that keeping orbitals FROZEN instead of CLOSED
> would always increase the total energy. Am I wrong?
>
> Lorenzo