From owner-chemistry /at\ccl.net Tue Mar 10 15:25:00 2009
From: "Steven Gwaltney gwaltney:-:ccs.msstate.edu" <owner-chemistry^server.ccl.net>
To: CCL
Subject: CCL: negative excitation energy in CCSD calculations
Message-Id: <-38808-090310134916-12211-AE8wisDk/WWA1+psRDEaTA^server.ccl.net>
X-Original-From: Steven Gwaltney <gwaltney###ccs.msstate.edu>
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Date: Tue, 10 Mar 2009 12:12:38 -0500
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Sent to CCL by: Steven Gwaltney [gwaltney.:.ccs.msstate.edu]
Negative EOM-CCSD or CCSD-LR excitation energies normally mean that the 
reference state is not the ground state of the molecule.  If the states 
which had the negative excitation energies can be described with a 
single reference determinant, I would suggest trying a (ground state) 
CCSD calculation on the states which gave the negative excitation 
energies, and comparing the energy to your reference state energy.

Steve Gwaltney

yz lan lyzhao|-|zjnu.cn wrote:
> Sent to CCL by: "yz  lan" [lyzhao : zjnu.cn]
> Dear all, 
>     I ran the CCSD calculation and got the two negative excitation energies.
> Could anyone give me any references about this problem or help me to make sure whether the results are meaningless.
> 
> Best regards,
> 
> lyzhao
> 
> 
-- 
Steven Gwaltney, Ph.D.               Phone: 662-325-7602
Associate Professor                    Fax: 662-325-1618
Department of Chemistry,              Mail: Box 9573
Center for Environmental Health Sciences,   Mississippi State University
and HPCC Center for Computational Sciences  Mississippi State, MS 39762