Hello, I have a question regarding the gaff.dat file used in OpenBabel for energy calculations and setting up force fields.
In OpenBabel, torsion terms seem to be defined in the format:
X -c -c -X 4 1.200 180.000 2.000
X -c -c1-X 2 0.000 180.000 2.000
X -c -cg-X 2 0.000 180.000 2.000 same as X-c-c1-X
X -c -ch-X 2 0.000 180.000 2.000
X -c -c2-X 4 8.700 180.000 2.000 intrpol.bsd.on C6H6
Where the is are I J K L atoms defined. Near the bottom of this list though, there is a line break and the format changes slightly to be more explicit in definition of I J K L and the second column disappears (what does this value represent?).
X -o -c -o 1.1 180. 2. JCC,7,(1986),230
X -X -c -o 10.5 180. 2. JCC,7,(1986),230
X -X -ca-ha 1.1 180. 2. bsd.on C6H6 nmodes
X -X -n -hn 1.1 180. 2. JCC,7,(1986),230
X -X -n2-hn 1.1 180. 2. JCC,7,(1986),230
X -X -na-hn 1.1 180. 2. JCC,7,(1986),230
X -c3-n -c3 1.1 180. 2. JCC,7,(1986),230
Are these the improper torsional terms or just a ‘exceptions’ list to the more general torsion terms? Furthermore, I noticed that there are duplicate atom-groups with different params:
c3-c3-c3-c3 1 0.18 0.0 -3. Junmei et al, 1999 c3-c3-c3-c3 1 0.25 180.0 -2. Junmei et al, 1999 c3-c3-c3-c3 1 0.20 180.0 1. Junmei et al, 1999
How do I know which one to use?
Thanks!
