Subject: CCL:SCF convergence criteria

From: "Jens Spanget-Larsen" <spanget:at:virgil.ruc.dk>
Date: Thu, 4 Sep 2003 09:59:52 +0200

Noel O'Boyle:

> Does anybody know or understand why the default SCF convergence
> criteria for single point calculations is looser than the default for
> geometry optimisations?

"SinglePoint" or "Sleazy" is an SCF option requesting 
relatively loose convergence criteria. It is the default for a 
a single point direct SCF or CASSCF calculation; I don't know 
excactly why. But evidently, a "single point calculation" 
should be considered as a fast, preliminary run. Otherwise, 
the option "Tight" should be selected, corresponding to 
normal, tight convergence in the SCF procedure. The latter is 
the default for everything except CASSCF and direct SCF single 
points (according to the manual). 
 
> In short, if you geometry optimise a structure, surely you should use
> SCF=Tight if you do a subsequent single point energy calculation. (Of
> course, you can avoid this question if you use Guess=Read.)

I agree.

Yours, Jens >--<

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JENS SPANGET-LARSEN         Office:         +45 4674 2710
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