AMBER Archive (2005)

Subject: AMBER: GAFF angle parameters

From: Monica Civera (monica.civera_at_unimi.it)
Date: Tue May 17 2005 - 11:11:46 CDT

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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