Subject: Re: CCL:G92 B3LYP calculations for iodine with ECP

From: <[email-masked]>
Date: Thu, 28 Sep 1995 14:43:00 -0400

> I'm performing G92 B3LYP calculations for iodine with  ECP and get the 
> following messages:
>
> "No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom. 
>  No unpruned grid is available for this atom." 
>
> I do get the job completed, but I'd really appriciate it if someone would 
> explain to me what this message means and what the consequences are.
>
> -Sergei

I was hoping someone more qualified would offer an explanation.  But since they 
haven't, I'll risk getting flamed....

I beleive the DFT contribution (numerical integartiuon) to the potential 
and correlation energy is computed on a grid of points which, in the case 
of G94/G94, is assembled from grids defined for each element.  Redundant 
points and nonsense locations, such as those "inside" other atoms, are 
necessarily discarded/ignored.  The process can be sped up by using "pruned 
grids", judiciously optimized reduced sets of grid points for each element. 
Pruned grids can impact the energy calculation but those supplied with well 
known codes should cause small or insignificant differences (=<+/-0.001 
hartree), apperently worth the trad-off with what I've heard is a 10-20% 
speedup in the computation of the DFT contribution to the energy.

In short, don't worry about the message.  They simply prompt users to bug 
developers about it so they don't forget to implement the pruned grids as 
and when they become available to speedup the calculations.

Hope thsi helps.  I appologise in advance for errors or misrepresentations.

Karl
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| Karl F. Moschner, Ph. D.                                              | 
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