TDDFT question



Hi,
 Does anyone has experience in TDDFT calculation on a charged molecule?
 I found that for neutral compounds, TDDFT generally gives smaller excitation
 energy than experiment for neutral compounds.  However, for charged molecules,
 it gives much, much higher energy.  Why?  Any suggestion?
 Thank you all in advance!
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 Jun Deng                                          440 College Park Drive
 Senior Research Chemist                   Monroeville, PA 15146
 Applied Scientific Computing                 Tel:  (724) 325-5243
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 PPG Industries, Inc.                        E-mail: jdeng ( ( at ) ) ppg.com
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