Subject: G94 DFT SCF Convergence Problems...

From: "Nathan A. Baker" <[email-masked]>
Date: Tue, 5 Aug 1997 10:53:35 -0700 (PDT)

Hi -- I'm using the BPW91 method with the 6-31G basis set to evaluate the 
single point energy of ~30 atoms surrounded by 10 point charges.  I've 
turned off the symmetry (the system was already C1 point group anyway) to 
avoid re-orientation of the molecule with respect to the point charges.

Without the point charges, the calculation takes 12 min of Power 
Challenge time.  Upon adding the point charges, I was unable to reach SCF 
convergence within the allotted 64 cycles.  I added the SCF=QC option, 
and received a "Spurious integrated density" error.  I added the 
recommended "Int=FineGrid" and "SCF=NoVarAcc".  This resulted in a eror 
indicating the necessary memory was unavailable.  I added the Link 0 
line, "%Mem=250MB" and once again had convergence problems (after a much 
longer wait).  Finally, I used:

#BPW91/6-31G SCF=(VShift,QC) Stable=Opt NOSYMM Charge

and after waiting 5 hours for what was once a 12 min. calculation, killed 
it.  I don't understand the problems that are occurring.  Basically, 
these charges just add a few more terms to the potential energy function, 
but don't add any more basis functions, right?

If anyone has any ideas on this problem, I'd be very appreciative.  I 
would like to continue to use the BPW91 method to keep things consistent 
with other calculations I've done.

Thanks!

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Nathan Baker * [email-masked]

HELP! MY TYPEWRITER IS BROKEN!
	-- E. E. CUMMINGS
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