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Re: ISPIN filter for doublet states

Alex Granovsky

Dear lello,

the ISPIN filter only works if the number of alpha electrons is equal
to the number of beta electrons and so unfortunately it cannot be used
for doublets.

Try increasing nhgss, nstgss, and mxxpan in $det/$cidet groups.

          NHGSS  = dimension of the Hamiltonian submatrix which
                   is diagonalized to obtain the initial guess
                   eigenvectors.  The determinants forming the
                   submatrix are chosen on the basis of a low
                   diagonal energy, or if needed to complete a
                   spin eigenfunction.  The default is 300.

          NSTGSS = Number of eigenvectors from the initial guess
                   Hamiltonian to be included in the Davidson's
                   iterative scheme.  It is seldom necessary to
                   include extra states to obtain convergence to
                   the desired states.  The default is the value
                   for NSTATE.

          MXXPAN = Maximum number of expansion basis vectors in the
                   iterative subspace during the Davidson iterations
                   before the expansion basis is truncated.  The
                   default is the larger of 10 or NSTGSS+1.  If this
                   value is decreased, convergence is hurt but the
                   memory required is decreased.

Hope this helps.

Kind regards,
Alex Granovsky

On Wed May 15 '13 5:05pm, lello wrote
>Hi all,
>I have read on the forum that it is possible to improve the convergence of SA-MCSCF using ISPIN keyword to generate a better selection of initial states (for ALDET method).
>ISPIN=0 filters all odd spin numbers  and ISPIN=1
>filters all even spin numbers.
>What about doublet states? Is is possible to improve the initial
>guess for doublets?


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