[molpro-user] mrci spin purity

[Peter Knowles]

In the MRCI code, pure spin-eigenfunction CSFs are used for the reference space, and for internal and singly excited configurations; for the doubly excited configurations, contracted functions are generated by operating on the reference wavefunction with purely spatial operators. Thus the wavefunction is constructed in a space of spin eigenfunctions.
Peter
> On 6 Feb 2015, at 18:56, Martin Spenke <martinspenke at yahoo.de> wrote:
> 
> Or how can i calculate expectation value of S^2 in molpro ?
> 
> 
> Martin Spenke <martinspenke at yahoo.de> schrieb am 17:05 Freitag, 6.Februar 2015:
> 
> 
> Is there any possible sign in case of symmetry breaking that could make me aware of the fact 
> that my targeted spin state is contaminated by higher spin multiplicities in contracted mrci ?
> 
> If no,  how can i run mrci in molpro without contraction to be able to compare the results of both methods ?
> 
> Martin
> 
> 
> Peter Knowles <KnowlesPJ at cardiff.ac.uk> schrieb am 8:29 Freitag, 6.Februar 2015:
> 
> 
> In the MRCI method, the energies are obtained from a linear eigenvalue problem. Thus provided that the hamiltonian matrix is a representation from a basis that is closed under symmetry operations (spin or space), its eigenfunctions will be symmetry pure.  In the contracted MRCI method, it is sometimes possible to arrange for this not to be true, but normally, with a reference wavefunction that is a definite symmetry, you should not expect symmetry breaking.
> 
> Peter
> 
> > On 5 Feb 2015, at 19:03, Martin Spenke <martinspenke at yahoo.de> wrote:
> > 
> > Dear all, 
> > 
> > is the mrci calculation in molpro purified from contributions of higher spin multiplicities
> > when computing excitation energy of a singlet spin state ?
> >  
> > Bests
> > Martin
> 
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> --
> Prof. Peter J. Knowles            
> School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
> Telephone: +44 29 208 79182
> Email: KnowlesPJ at Cardiff.ac.uk 
> 
> Yr Athro Peter J. Knowles
> Yr Ysgol Cemeg, Prifysgol Caerdydd,
> Prif Adeilad, Plas y Parc
> Caerdydd CF10 3AT, DU
> Ffôn: +44 2920 879182
> Ebost: KnowlesPJ at Caerdydd.ac.uk
> Ysgrifennwch ataf yn Gymraeg neu Saesneg
> 
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--
Prof. Peter J. Knowles             
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
Telephone: +44 29 208 79182
Email: KnowlesPJ at Cardiff.ac.uk 

Yr Athro Peter J. Knowles
Yr Ysgol Cemeg, Prifysgol Caerdydd,
Prif Adeilad, Plas y Parc
Caerdydd CF10 3AT, DU
Ffôn: +44 2920 879182
Ebost: KnowlesPJ at Caerdydd.ac.uk
Ysgrifennwch ataf yn Gymraeg neu Saesneg