[gmx-users] Improper dihedrals in Charmm FF

Peter C. Lai pcl at uab.edu
Wed May 25 14:39:10 CEST 2011

On 2011-04-21 03:54:09AM -0500, Jianguo Li wrote:
> Dear all,
> My molecule contains -CH=CH- fragment and I am trying to create the topology using Charmm FF. It seems that there is no improper dihedrals for -CH=CH- fragment in Charmm FF, while other FF (e.g., Amber or OPLS) has additional improper dihedrals terms for that fragment.
> Could anybody confirm this?

AFAIK, CHARMM only defines impropers for planar fragments not linear ones...
(based on my reading of CGenFF2b6)

This sort of makes sense since in a linear structure, normal dihedrals are
already defined for every meaningful combination...

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