[molpro-user] Calculating molecular oxygen excited state
Lorenzo Lodi
l.lodi at ucl.ac.uk
Mon Sep 28 19:52:44 BST 2009
Jacky LIEVIN wrote:
> Dear Lorenzo,
>
> Please find below a modified version of your input. The results are
> looking fine:
[cut]
Thanks a lot Jacky, it did the trick and it's now working fine!
I spent some time studying your sample input (I'm new to state-averaged
calculations) and there a few things I'm not too sure of.
For the excited-state state-averaged CASSCF your input reads:
{MCSCF;
WF, NELEC=16, SYMMETRY=1, SPIN=0;state,2;lquant,2,0
WF, NELEC=16, SYMMETRY=1, SPIN=0;state,1;lquant,2}
The second line specifies the two lowest-states with "1" (=Ag) symmetry,
namely the <sigma g+> and <delta g xx-yy>.
If the third line is to specify the degenerate <delta g xy> state with
symmetry "4" (=B1g), shouldn't we specify SYMMETRY=4 ?
Also, I have a slightly different question. Is it advisable/necessary to
in the excited-state RHF step to have it to converge to the desired
excited state too? Couldn't we use the ground state as RHF reference for
the subsequent steps?
Thanks again,
Lorenzo
> Modifications are:
> 1) the use of state averaged MCSCF
> First for ensuring the degeneracy of the delta state (one component of
> symmetry 1 and one of symmetry 4): group theory tells us that deltag
> correlates to Ag + B1g in D2h symmetry
> Second for describing the second state (sigma + g) of symmetry 1:
> sigma + g correlates to Ag
> Both electronic states must thus be calculated in a single MCSCF state
> averaged calculation defined by 2 WF directives.
> Note the lquant directive given on each WF line and for each
> calculated state
> Note the degeneracy CASSCF(1)=CASSCF(2)= energy of delta state
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