Subject: bsse procedure using Gaussian 98

From: "�� �ƴ�" <[email-masked]>
Date: Sun, 1 Oct 2000 16:57:37 +0800 (CST)

Dear cclers:

    Can you tell me if this process  is  coerrect?Sincerely need your help. 
Take it for example we use hf/6-31g* 

  Basis Set Superposition Error (BSSE) 
              Correct the dimerization energy for BSSE using the Counterpoise (CP) method.        
   1.Etot Dimer (opt. geom.)  
 the energy from the hf/6-31g* optimized supramolecule                2.Etot 2*Monomer (opt. geom.)   the energy from hf/6-31g* optimized monomer                     
3.EtotDonor (opt. geom. of dimer, with ghost basis at the acceptor)  hf/6-31g* using Massage
4.Etot Acceptor (opt. geom. of dimer, with ghost basis at the donor)    hf/6-31g* using Massage   
5.Etot Donor (opt. geom. of dimer,without any ghost basis)                        6.EtotAcceptor (opt. geom .of dimer, without any ghost basis)               using hf /6-31g* to do single point calculation   on the 
  monomer with the deletion of other monomers in Suparmolecule    

      BEuncorr = 1 - 2       BEcorr = BEuncorr - (3 - 5) - (4 - 6)

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From: uccatvm <[email-masked]>
Date: Sun, 1 Oct 2000 19:24:27 +0100 (BST)

>     Can you tell me if this process  is  coerrect?Sincerely need your hel=
> p.=20
> Take it for example we use hf/6-31g*=20
> 
>   Basis Set Superposition Error (BSSE)=20
>               Correct the dimerization energy for BSSE using the Counterp=
> oise (CP) method.       =20

Your procedure is in principle correct; it is the correct way of computing
the counterpoise-corrected interaction energy at a particular geometry.

You have probably optimized the dimer geometry without counterpoise
corrections, and in that case, this geometry may still be contaminated
with BSSE (because the counterpoise-corrected and uncorrected potential
energy surfaces will be shaped differently. How much, that depends on
the particular molecular system you are investigating).
In principle, you'd have to optimize the dimer geometry on the
counterpoise-corrected potential energy surface (see for example
S. Simon, M. Duran, J.J. Dannenberg, J. Chem. Phys. 105, 1996), 
but this is computationally more complicated, and more expensive as well.

Hope this helps,

Tanja
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