[gmx-users] Can Ryckaert-Bellemans(RB) function be used to calculate improper dihedrals?

[michael.b]

i was wondering about the same question ... 
from using antechamber and amb2gmx.pl output in
simulations i concluded that this seems to work, in other
words the R-B dihedrals are in fact used for improper 
dihedrals, you can check by looking at your topology
files ... for improper dihedrals the central atom is usually
the third (ak) of the four numbers in your topology file ...

[ dihedrals ]
;  ai    aj    ak    al funct            c0            c1            c2           
c3
    3     2     1     5     3    myimp-x-x-x-x

the fact that this comes under the heading [ dihedrals ] is confusing
but harmless in my experience ..

if you use pdb2gmx you also need to make sure that in the top section
of your rtp file type 3 is requested for impropers!

cheers
mic



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