On Wed, Mar 01, 2006, Mark Williamson wrote:
>
> 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?
This is pretty useful if you want to see the limitations of the simple gaff
model, or as a starting point for improvements for individual molecules.
You might consider first applying a scaling factor to the Gaussian frequencies
(to bring them more into line with experiment), and/or using a DFT model like
B3LYP, which will generally have better frequencies.
...good luck...dac
--
==================================================================
David A. Case | e-mail: case.scripps.edu
Dept. of Molecular Biology, TPC15 | fax: +1-858-784-8896
The Scripps Research Institute | phone: +1-858-784-9768
10550 N. Torrey Pines Rd. | home page:
La Jolla CA 92037 USA | http://www.scripps.edu/case
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Received on Sun Mar 05 2006 - 06:10:12 PST
