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Understanding the GAFF Force Field

Asked by , Edited by Eric Jang

Hello, I am trying to port the GAFF force field from data/gaff.dat and data/gaff.prm to be read by another program (TINKER). However the parameter file of GAFF looks quite different than from MMFF94 or any of the other force fields. I was wondering if someone could explain to me the difference...

I ask this because AMBER and OpenBabel have the same .dat/.prm file for GAFF, whereas I am looking for the structure where the numbers are listed by atom type in the categories below (such as in MMFF):

# atom properties

# fallback defs

# bond stretching parameters

# angle bending parameters

# empirical rule parameters (bond stretching)

# charge parameters

# empirical rule parameters (bend-stretch)

# out-of-plane parameters

# partial bond charge increments

# strech-bend parameters

# torsion parameters

# van der waals parameters

I just learned that GAFF's functional form of calculation is different, in calculating the above parameters. How difficult would it be to re-write those functions to accomodate GAFF params?

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