[molpro-user] <S**2-Sz**2-Sz>

[Peter Knowles]

Yes, there is: the spin contamination is zero. The MRCI code uses the same orbitals for alpha and beta spin, and this implies that the many-electron basis set spans complete spin spaces. Because the CI ansatz is a linear matrix eigenvalue problem, the fact that S^2 commutes with the hamiltonian then guarantees that the eigenvector of the hamiltonian is also an eigenfunction of S^2.

Peter

On 25 Mar 2011, at 09:07, Jiri Czernek wrote:

> Hi,
> 
> I'm very sorry if this is a FAQ but ... Any way of estimating the spin 
> contamination of the MR-CI wavefunction, <S squared> at least, thanks ...
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Prof. Peter J. Knowles             
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