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.
Tanja
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.
Gerd
From: uccatvm <uccatvm (+ at +) ucl.ac.uk>
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: T.vanMourik (+ at +)
ucl.ac.uk
London WC1H 0AJ, UK home: tanja (+ at +)
netcomuk.co.uk
http://www.chem.ucl.ac.uk/people/vanmourik/index.html
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