Ceilidh ... Re^2: Geometry optimization of S1 state by MCSCF

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Re^2: Geometry optimization of S1 state by MCSCF

Dear Prof. Granovsky,
Thank very much for your time and for example files. I have known that the state-
averaged MCSCF is used to avoid 'root-fliping'. Any way, I have some questions for
the example file of opt.s1.sa.inp (here,I confirm that absence of MULT in $CONTRL
means singlet-state computation).

>! Need extra states in CI as the second one is triplet
> $DET NCORE=7 NACT=2 NELS=2 NSTATE=4 GROUP=C1 ITERMX=200
>PURES=.T. $END
I understand that PURES=.T. means that only singlet states are included in the
state-averaging. Is this understanding correct? The sentence of 'the second one is
triplet' makes me confused. Why the triplet state appears in this case? Moreover,
how did you determine the number of states of four, that is, how did you determine
NSTATE=4 before doing this run?

! State-averaged MCSCF
$DET WSTATE(1)=1,1 $END
! istate=2 means we need properties and gradiends of second state (S1)
$mcscf CISTEP=aldet maxit=200 ISTATE=2 $end
The expression of 'second state (S1)' also makes me confused, because this seems to be
inconsistent with the above sentence 'the second one is triplet'. I imagine that the
triplet state is removed and thus the S1 state is 2nd lower state among all singlet
states. Is this correct?

In opt.s1.sa.out
STATE 2 ENERGY= -113.6672881517 S= 1.00 SZ= 0.00 SPACE SYM=A
ALPH|BETA| COEFFICIENT
----|----|------------
01 | 10 | -0.7071068
10 | 01 | 0.7071068
10 | 10 | 0.0000000

I think that the above combinations of ALPHA and BETA should be of singlet states.
But S= 1.00 is output. Why? (I think that this means 2S+1=3)

Best, regards,
Fumihito Mohri
Kaneka Corportaion, Japan

Mon Nov 17 '08 5:03pm

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