AMBER: Nmode vs QM Freq Calculation

From: Mark Williamson <>
Date: Wed, 01 Mar 2006 11:28:57 +0000

Dear Amber users,

When one is parameterizing for a small molecule say using the GAFF, how
useful is the comparison between frequencies obtained from NMODE for
that parameterization, and the QM "normal mode" frequencies from say a
HF/6-31G* Guassian "opt freq" calculation?

Of course, there is not IR absorption information, but should the value
of the frequencies generally agree?

Could this be considered a useful sanity check for a parameterization or
is the situation more complex?


Mark Williamson
The AMBER Mail Reflector
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Received on Sun Mar 05 2006 - 06:10:12 PST
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