Getting rs2 to find the desired ref state

[Paolo Celani]

You can try to increase the number of p-space configurations
with keyword 'pspace' up to a maximum number of 100 (section 16.4.9).
The 13 configurations chosen in the calculation probably described
poorly the 7th root. 

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> Getting rs2 to find the desired ref state
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>    * To: <molpro-user at tcpc3.bham.ac.uk>
>    * Subject: Getting rs2 to find the desired ref state
>    * From: "Falcetta_Michael" <Falcetta_Michael at roberts.edu>
>    * Date: Fri, 21 Sep 2001 12:05:35 -0400
>    * Sender: owner-molprouser at tc.bham.ac.uk
>    * Thread-Index: AcFCtz9trdzZLaXBEdW5mABQBAUEcA==
>    * Thread-Topic: Getting rs2 to find the desired ref state
> 
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> Dear molpro users,
> 
> I am trying to do a rs2 calculation on the 6,7,&8th roots derived from
> an mcscf.  The mcscf energies are
> 
> Root   MCSCF ENERGY
> 6       -114.88831918
> 7       -114.86572251
> 8       -114.83010692
> 9       -114.75248957
> 
> When I take the state averaged canonical orbitals fromt the mcscf (and
> use the same config list for the ref space of the rs2 as I used in the
> mcscf), the rs2 module find the following:
> 
> Number of p-space configurations:  13
> 
>  Reference wavefunction optimized for reference space (refopt=1)
> 
>  State     Reference Energy
>    6        -114.88831918
>    7        -114.83010692
>    8        -114.75248951
> 
> Clearly RS2 has missed what was the 7th root in the mcscf!!
> 
>  If I ask the RS2 to extract 10 roots it does correctly find the 7th
> root to correspond to the 7th root in the mcscf (i.e., the p-space does
> contain the correct root and it is calculating the reference energy
> correctly)
> 
> My question is: Is there an efficient way to get the RS2 program to get
> the correct roots?  I think I will need to extract roots 6,7,&8 because
> at certain geometries these roots will be close in energy and may cross,
> but how can I ensure that the RS2 calculation gets the correct roots.
> 
> Thanks in advance
> 
> Mike
> 
> Dr. Mike Falcetta
> 
> Associate Professor of Chemistry
> Roberts Wesleyan College
> 2301 Westside Drive
> Rochester, NY 14624
> 
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