AMBER Archive (2007)

Subject: Re: AMBER: Dihedral FF parameters

From: Ye Mei (ymei_at_itcc.nju.edu.cn)
Date: Fri Jan 19 2007 - 09:44:14 CST

DFT is not variational.

        
Best regards,
                                 
Ye Mei
ymei_at_itcc.nju.edu.cn
Institute of Theoretical and Computational Chemistry
Key Laboratory of Mesoscopic Chemistry
School of Chemistry and Chemical Engineering
Nanjing University
Nanjing 210093
P.R.China
2007-01-19

======= 2007-01-19 23:40:10 FyD wrote=======

>Dear All,
>
>I try to develop a bunch of new FF parameters by fitting MM energies
>to QM energies. As first tests, I decided to fit the FF dihedral
>parameters to data generated to the B3LYP/6-31+G**/HF/6-31G* &
>MP2/6-31+G**//HF/6-31G* theory levels. Since my model is a little big,
>I think I cannot afford MP4 energies.
>
>In FF development and to get QM single point energy, what theory level
>is the best, I mean for taking into account electron correlation: MP2
>or B3LYP ?
>
>I would answer MP2, however I was quite surprised to see that the
>B3LYP energies are smaller than the MP2 ones.
>
>Thank you, regards, Francois
>
>
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