PC GAMESS/Firefly-related discussion club

Re: Geometry optimization of S1 state by MCSCF

Alex Granovsky


I've attached the samples of CASSCF (2,2) geometry optimization
of S0 and S1 states for your system using both state-specific and
state-averaged MCSCF.

Note that for S1 with state-spcific CASSCF, optimization failed
as CASSCF did not converge - this is quite a common situation
for excited states. In this particular case, the reason of
failure is the quasi-degeneracy of S0 and S1 at some geometries.

I'd then recommend you to use SA-CASSCF, which is much more stable.

The proper selection of active space is very important.
CAS (2,2) is natural for your problem. You can use larger spaces
but be careful to select proper orbitals!

And sure, you can use $guess norder=1 iorder(1)=... to reorder orbitals.

Alex Granovsky

On Sun Nov 16 '08 5:36am, Fumihito Mohri wrote
>Dear PC-GAMESS users

>I am studying MCSCF method.  My final target is computation of
>spin-orbit coupling constants for organic optical matetials.  
>Now, I am facing a problem with MCSCF job for HCHO molecule(this is an
>excersize job).
> Attached file is an input file. This HCHO molecule is not co-planar.
>$VEC data was obtained by RHF/6-31+G(d) for this molecule. The number
> of electrons is 16, thus HOMO is the 8th MO. The active space consists
> of 7th, 8th, 9th and 10th MOs (i.e. CASSCF(4,4)). Symmetry is chosen
>as C1. From this file, I want to obtain optimized geometry and energy
>of S1 (the first excited singlet state). But, this input file brings
> only S0 result (i.e. ground state result).  Could you tell me what is
> wrong with this file. I do not yet well understand the relationship
> between  NSTATE, IROOT and SZ.
>  I have one more question. In Gaussian, MO alternation is sometimes done
> by Guess=Alter to make an appropriate active space. Does PC-Gamess have
>the keyword corresponding to Guess=Alter?

>Thank you in advance

This message contains the 119 kb attachment
[ ch2o_s0_s1.rar ] SS and SA MCSCF geometry optimization samples for CH2O

[ This message was edited on Sun Nov 16 '08 at 10:53pm by the author ]

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