AMBER Archive (2005)

Subject: RE: AMBER: GAFF angle parameters

From: Junmei Wang (jwang_at_encysive.com)
Date: Tue May 17 2005 - 17:08:47 CDT


Hi, there,
 
Please check the erratum on "JOURNAL OF COMPUTATIONAL CHEMISTRY 26 (1):
114-114 JAN 15 2005" to find the correct formula to calculate the force
constant.
 
All the best
 
Junmei
 
Dear all,

         
        According to the empirical equation reported in the article
about Development of a General Amber Force Field, J. Compu Chem. 2004, I
am trying to parameterize the bond angle and the constant of the missing
s6-c3-c3 (atom types) angle of Taurina. The MP2(6-31G*) results on the
two models molecules are not very different from the GAFF angle and bond
distances parameters but I am not able to obtain a sensible result for
the bond angle force, also replacing the GAFF parameters:
         
        GAFF parameters substituted:
         
            
Zs* Cc*
Zc*
r S-C
r C-C
theta**
c3-c-s6(rad)
1.28
1.339
1.183
1.76
1.53
1.9305965
         
            *taken fron the article
         
            **Theta= 0.5(tetha(c3-c3-c3)+tetha(s6-c3-s6)
         
        Resulting angle force costant:
         
        K(GAFF)=23.562 kcal/mol rad(-2)
         
        I expected a constant K in the range of 50-70 kcal/mol rad(-2).
I would like to know where is my fault.
         
        Thanks!

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