[molpro-user] why diffuse functions are such efficient

[MHT]

Thank you all very much! ^_^
I forgot to say that I did optg at multi,
and this geom is used for SP calculation at mrci.

geom from vqz and avqz are almost same, which are very closed to exp. 
values.

On Fri, 16 Jun 2006, Kirk Peterson wrote:

> 
> It's a little difficult to tell without knowing what A and B actually  
> are, but I
> would guess that in the avqz multi calculation you might have  
> converged to the
> wrong state in the separated A+B part or likewise you converged to  
> the wrong
> state in the vqz calculation for the molecule. I'd check the orbitals  
> carefully.
> 
> Again without knowing what AB is it is difficult to say for sure, but  
> I would say in
> most cases such an excellent dissociation energy with MRCI in just a  
> vdz basis
> set must be fortuitous (or the experimental value is inaccurate).
> 
> just my 2 cents,
> 
> -Kirk
> 
> On Jun 15, 2006, at 8:05 PM, MHT wrote:
> 
> >
> > Dear Molpro User,
> >
> > I am calculating D_0, here D_e(A-B)=[E_(A) + E_(B)] - E_(AB).
> > Both A and B are doublet radical, AB is a stable molecular.
> > active space in multi is full valence.
> > By, vqz at multi, the D_e(A-B)=79.77kcal/mol,D_o(A-B)=72.48kcal/mol;
> > By, avqz at multi, the D_e(A-B)=106.54kcal/mol,D_o(A-B)=98.332kcal/ 
> > mol;
> > However, mrci/vdz give D_e(A-B)=93.12kcal/mol,D_o(A-B)=85.83kcal/mol,
> > using ZPE from multi/vqz.
> >
> > the exp value D_o(A-B)=86kcal/mol.
> >
> > puzzle:
> > 1.Why there is so much different between vqz and avqz results?
> > 2.Why mrci gives such good result? coincidence?!
> >
> > thank you and wish all have a very nice weekend!
> > MHT
> >
> > -- 
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> > =====================================================
> >
> >
> 

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