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How do I get a better initial guess (SnI3)?

David Shobe

How can I improve on GUESS=HUCKEL when it fails to perform?

At least I'm assuming the initial guess is at fault and not the choice of parameters EXTRAP DAMP SHIFT DIIS and SOSCF. This is because from beginning to end of the DFT orbital calculation, I am getting wildly different energies from one iteration to the next.

I tried SnI3+ (which is a closed shell), but got the same result. So my question is: now what?

I could try to swap occupied and unoccupied orbitals with NORDER, but I'm flying blind.

If you're wondering: Yes, I do have diffuse functions. SnI3 converges fine when you omit them.  But I think I need the diffuse functions for accuracy.

Regards, and thanks for any help,
--David Shobe

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