Summary) QCISD/LanL2DZ

Hello, CCLers.
 I sent following question a few days ago.
 > I like to use QCISD/LanL2DZ for geometry optimization of heavy
 > rare gas atoms system on Gaussian98W.
 >  example:
 >
 >     # QCISD/LanL2DZ Opt
 >
 >     Opting
 >
 >     Ar             0.000000      0.000000     0.000000
 >     Xe             5.000000     0.000000      0.000000
 >
 > When I calculate with QCISD/LanL2DZ, what things should I take
 > into account ?
 > When I receive replies, I will summarize them.
 I've receive two good replies. Thank you so much Dr. Per-Ola Norrby
 and Dr. Tanja van Mourik.
 Their advices include common notice to consider BSSE. And, with Norrby's
 words, I must find out suitable basis set.
 <<<<< Summary  >>>>>
 1) from Per-Ola --------
 Mainly that all your results will be seriously wrong, since
 the basis set is much too small for a correlated calculation.  I
 assume you want to see the vdW interaction, and it will be completely
 overshadowed by the BSSE.
 And no, I don't have a good basis set, you'll have to look
 for that in the literature.
 Best regards,
 Per-Ola Norrby
 2) from Tanja --------
 Please note that the BSSE is likely going to be large for a system
 like this, and will affect the equilibrium distance. It would therefore
 be better to optimise with counterpoise corrections.
 With Gaussian03 this can be done automatically (using the Counterpoise
 option), but with Gaussian98 you'd have to do it by hand. Just calculate
 a counterpoise-corrected potential energy curve by calculating the
 counterpoise-corrected Ar-Xe interaction energy at a range of different
 Ar-Xe distances. See for example:
 T. van Mourik, A.K. Wilson, K.A. Peterson, D.E. Woon and T.H. Dunning,
 Adv. Quant. Chem. 31, 105-135 (1999) or
 T. van Mourik, A.K. Wilson and T.H. Dunning, Mol. Phys. 96, 529-547 (1999).
 Hope this helps,
 Tanja
   Sincerely yours,
 ------------------------------------------------------
        Telkuni Tsuru     telkuni..at..venus.dti.ne.jp