Subject: open-shell force fields

From: [email-masked] (Thomas Bally)
Date: Tue, 22 Nov 1994 15:37:19 +0100

Dear Netters,

  we are attempting to fit force fields of open-shell species (triplet
carbenes, radicals, radical ions) starting from Hessians computed by
some quantum chemical procedure and we face the problem that UHF and
ROHF often give *very* different valence force fields (in spite of the
fact that the geometries often do not differ that much). In cases of
large <S**2> values, we wish to avoid UMP2 and the available R(O)MP2
codes (Cadpac, Aces) often give us nonsensical results.

  Is anyone aware of any systematic studies which have been conducted
to assess the reliability of ROHF vs. UHF (or any other methods such
as DFT) for force fields or vibrational frequencies of open-shell species?

  Please reply to my personal e-mail address, I will post a summary to
the net if I get any useful hints.

  Thanks for your help!

  thomas

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|  Prof. Thomas Bally                 |  E-mail:  [email-masked]   |
|  Institute for Physical Chemistry   |                                   |
|  University of Fribourg             |                                   |
|  Perolles                           |  Tel:     011-41-37 826 489       |
|  CH-1700 FRIBOURG                   |  FAX:     011-41-37 826 488       |
|  Switzerland                        |                                   |
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