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** Re^3: SCF problems **
Alexei Popov

alexei.a.popov@gmail.com

Hello Pedro,at your geometry, the energies of double-filled HOMO and

single-occupied orbital are almost identical; and this is

the origin of the problems you have encountered. There

exist at least two different solutions of SCF equations

nearly this particular geometry.

You can try to use SOSCF instead of DIIS. Alternatively,

restrict orbital mixing and increase the value of fshift, e.g.:

$scf
diis=.t. dirscf=.t. diis=.t. rstrct=.t. shift=.t. fshift=0.2
$end

The latter will in general have negative impact on the

convergence rate. As to SOSCF, it will have some problems

at the first geometry, but should rapidly converge at the

subsequent ones.

You may need to use multi-configuration methods to describe this system well.

regards,

Alexei

On Tue Sep 28 '10 10:25pm, Pedro Silva wrote

--------------------------------------------

>Symmetry is C1..

>The input follows as attachment. I have tried changing convergers to SOSCF , disabling DIIS, changing ICUT/ITOL, FDIFF=.f. or FDIFF=.t. (always without success)

Mon Oct 4 '10 1:36pm

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