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Date: Wed, 05 Jul 1995 17:03:21 -0500 (EST)
From: Kui Zhang <KZHANG%MIAMIU.BITNET |-at-| phem3.acs.ohio-state.edu>
Subject: BSSE Correction for Protonation Energy
To: Computational Chemistry List <chemistry(+ at +)ccl.net>
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Dear Netters,
 
     One of our projects is the calculation of protonation energy
for some interesting compounds using high level ab initio calculations.
Recently I have been trying to correct calculated protonation energies
with BSSE.  I first used CH3NH2 as model compound to do testing
calculations at HF, MP2 and MP4 levels with several basis sets.  The
calculations were carried out using Gaussian 92 with MASSAGE method.
The following is a set of calculated values of the BSSE correction for
CH3NH2:
                                         BSSE Correction (kcal/mol)
 
HF/6-31G*//HF/6-31G*                             0.60
HF/6-31+G**//HF/6-31+G**                         0.84
HF/6-31+G(2d,2p)//HF/6-31+G(2d,2p)               0.31
MP2/6-31+G**//HF/6-31+G**                        6.87
MP4/6-31+G**//HF/6-31+G**                        7.20
MP2/6-31+G**//MP2/6-31+G**                      14.15
 
    It can be obviously seen that the MP and HF give a such huge
difference that there is absolutely not comprimise between HF and MP
values.  The same situation was also observed in another compound
similar to CH3NH2.  Can any of you help me handle this problem?  My
question is that which method I should trust in term of the BSSE
computation, MP or HF?  I would greatly appreciate any direction,
suggestion and comment.  Thank you very much in advance.
 
 
Kui Zhang
Department of Chemistry
Miami University
Oxford, OH 45056
USA
E-mail to: kzhang |-at-| miamiu.acs.muohio.edu