[molpro-user] active space

[Terry Frankcombe]

I have had a similar problem when trying to look at excited states in
sigma radicals where there is also a heap of pi bonding in other parts
of the system.

Essentially, the problem is that Molpro's MCSCF algorithm is too good.
Bringing in these other orbitals, at the expense of the part of the
system you're really interested in, increases the calculated correlation
energy and drops the total energy.

What has mostly worked for me is to tell multi to be a bit more stupid
and use the older augmented Hessian method.  That's well known for
getting stuck in local minima... which is exactly what you want here!
You tell multi to do this through the iterations directive.

Ciao
Terry


On Thu, 2010-09-09 at 19:17 -0400, lydia wrote:
> Dear all,
> I have a question about active space in the CASSCF calulations. I
> found that some empty orbitals which are not the ones I want will mix
> with the active empty orbitals I choose with almost equal
> contribution. Probally because those empty orbitals have similar
> energies with these avtive orbitals I choose. If it has small
> contribution, it can be ignored. But it is big in this situation. How
> do you usually solved this problem? If you have similar experiences,
> please share with me.
> Thank you.
> 
> All the best,
> lydia
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-- 
Dr. Terry Frankcombe
Research School of Chemistry, Australian National University
Ph: (+61) 0417 163 509    Skype: terry.frankcombe