Re: CCL:counterpoise with LMP2

 Dear All
I'd like to point out that the SCF-MI method is actually from A. Famulari, M. Raimondi, M. Sironi, E. Gianinetti (and recently has been reformulated by S. Iwata in a more compact fashion). With this method, the uncorrected and BSSE-corrected interaction energies do not approach asimptotically each other improving the basis set, since some physical delocalizations are removed from the SCf calculation Mayer's approach is the Chemical Hamiltonian Approach (CHA), which has been proved to be free of such pitfalls. (See for instance, "The Chemical Hamiltonian Approach for treating the BSSE problem of intermolecular interactions" I. Mayer Int. J. Q. Chem. 1998 70 41 )
 uccatvm wrote:
 Hi Gerd,
 Thank you for your answer. However, my question was more specifically how
 to get the best orbital domain match for the dimer and monomer+ghost
calculations in local MP2, and not so much how to do counterpoise calculations in general.
 The SCF-MI methods of Mayer and co-workers are a different approach to
deal with BSSE, and are not without problems. For example, with SCF-MI/VB method and the aug-cc-pV5Z basis set, the De of He2 is 10.64 K at 5.8 bohr - J. Mol. Struct. (Theochem) 549, 77, 2001. The FCI/aug-cc-pV5Z estimate is 10.17 K at 5.6 a.u. (J. Chem. Phys. 111, 9248, 1999). I think this shows that SCF-MI overestimates the interaction energy.
 maybe the work of Istvan Mayer et al.
  author = 	 {I. Mayer and \'A. Vib\'ok and G. Hal\'asz and P. Valiron},
  title = 	 {A BSSE-Free SCF Algorithm for Intermolecular
 		  Interactions. III. Generarlization for Three-Body
 		  Systems and for Using Bond Functions},
  journal = 	 {Int. J. Quantum Chem.},
  year = 	 {1996},
  volume =	 {57},
  pages =	 {1049}
 (see also the references there) is useful for you. This approach is
 especially useful if you are going to use small basis sets.  Here you
 also get a BSSE free wave function. Furthermore as far as I know you
 will find also a discussion how the classical Boys Bernardi Method
 should be applied - this should be sufficient if you just go for BSSE
 free energies.
   From: uccatvm <uccatvm (+ at +)>
   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 van Mourik Royal Society University Research Fellow Chemistry Department University College London phone: +44 (0)20-7679-4663 20 Gordon Street e-mail: work: T.vanMourik (+ at +) London WC1H 0AJ, UK home: tanja (+ at +)
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