Subject: counterpoise with LMP2

From: uccatvm <[email-masked]>
Date: Mon, 13 May 2002 21:56:43 +0100 (BST)

Hi all,

I am wondering what the most correct way is to do counterpoise with local 
MP2. In the local MP2 method originally proposed by Pulay (Chem.Phys.Lett. 
100, 151, 1983), to each localised MO a subset (orbital domain) of the 
virtual orbitals is assigned.  To calculate the interaction energy of a 
weakly interacting system, the orbital domains of the subsystems are first 
determined at large distance, and used in subsequent dimer calculations at 
smaller intermolecular distances (as recommended in for example Schutz et al., 
J. Phys. Chem. 102, 5997, 1998).

Now, I assume that (to keep a true counterpoise) it is best to use the 
orbital domains determined at large distance for the monomer+ghost 
calculation. For this, one would first have to determine the domains of the 
monomer+ghost with the ghost at large R, and use the thus obtained orbital 
domains in the monomer+ghost calculation at the smaller distance. What 
do people think? Would this be the correct way of doing it?

Of course, the BSSE is strongly reduced in LMP2, and should in principle
be negligible when using an appropriate basis set. However, when using 
small basis sets it may not be negligible, and I would like to know the 
best way of doing counterpoise for these cases.

Thanks in advance,

Tanja

-- 
  =====================================================================
     Tanja van Mourik                                                
     Royal Society University Research Fellow
     Chemistry Department 
     University College London    phone:    +44 (0)20-7679-4663      
     20 Gordon Street             e-mail:   work: [email-masked] 
     London WC1H 0AJ, UK                    home: [email-masked]     

     http://www.chem.ucl.ac.uk/people/vanmourik/index.html
  =====================================================================