Subject: H-bonded clusters

From: "Dr. Sudhir A. Kulkarni" <[email-masked]>
Date: Mon, 07 Oct 2002 17:03:25 +0530

Hello,
    We are working H-bonded clusters of some small molecules using
Gaussian 98.  We found that clusters up to n=2-4 are quite easy to get
and are optimized at both RHF and MP2 level (using 6-31++G** and CC-pVTZ
basis).  However for n=5 or 6 we face a peculiar problem: we find
several structures that are true minima (all frequencies positive) at
RHF level, however when we optimize these structures using MP2 method
they have more than 5 negative frequencies.
    I would like to know if anyone else has such experience & whether
there is any solution to this problem.
Thanks.

Sudhir

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