Subject: Re: BSSE should not affect gradient

From: uccatvm <[email-masked]>
Date: Fri, 13 Aug 1999 14:26:37 +0100 (BST)

Dear Teerakiat,

>    Question is ..... does BSSE affect gradient ? Is there
> any theory or paper doing on this issue ? I need only
> the answer but some clever man could take this to make
> a publication.

I don't agree with your assumption that the gradient is not 
affected by BSSE. The uncorrected and corrected potential energy 
surface have a different shape, and hence, the gradients will differ. 
If the gradient would be BSSE-free, one could optimize the geometry of 
a molecular system AB by minimizing the uncorrected energy Eab, and it 
well-known that this may lead to wrong geometries (generally, too short 
equilibrium distances Rab). 

As a further indication, if the gradients of the corrected and uncorrected 
surfaces would be the same, then the second derivatives, and therefore the 
frequencies, would also be the same, and it has been demonstrated that 
frequencies are also affected by BSSE. 

There are many publications addressing this issue. To name a few:

-  F.B. van Duijneveldt, J.G.C.M. van Duijneveldt-van de Rijdt, and
   J.H. van Lenthe, Chem. Rev. 94, 1873, 1994 (on counterpoise theory)

-  S. Simon, M. Duran, J.J. Dannenberg, J. Chem. Phys. 105, 1996 
   (on geometry optimizations on BSSE-corrected potential energy surfaces).

-  T. van Mourik, A.K. Wilson, K.A. Peterson, D.E. Woon, T.H. Dunning, Jr.,
   Adv. Quant. Chem. 31, 105, 1999 (showing BSSE effects on interaction 
   energies, distances, and frequencies).

HTH.

Best regards,

Tanja
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     Tanja van Mourik                                                
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