[gmx-users] angle restraints

[Maarten Wolf]

Dear users,

I have a small system with a number of small peptides. I want to
constraint the angle between the N-term to C-term vectors of different
peptides. This works well, but if I do a FEP calculation the dG/dl
becomes smaller than zero at some point. 
I expected it to be at least allways greater than zero (zero in the
limit that the restraint does not have to do anything), since a force
has to be aplied to restraint the angles. 
Can anybody explain where I am going wrong? 

Thanks
Maarten

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