[gmx-users] wrong calculation of dihedral angle with angle restraint?

Tomas Kubar tomas.kubar at uochb.cas.cz
Fri Nov 25 15:48:37 CET 2005

David wrote:

>On Wed, 2005-11-23 at 18:07 +0100, Tomas Kubar wrote:
>>I'm trying to restrain a dihedral angle (i-j-k-l) to -24 deg. In the 
>>course of the simulation, the structure of my molecule gets distorted 
>>rapidly and the simulation itself crashes with segfault; it seems that 
>>the function low_angres() in src/gmxlib/bondfree.c calculates the 
>>dihedral angle in a wrong way - only as the angle of vectors ij and kl. 
>>This angle differs from the definition of a dihedral angle (maybe it 
>>even lies in the interval 0-180 deg) and consequently, the desired value 
>>is not reached.
>>Do you think my interpretation is right?
>do you use angle restraint or dihedral restraints? For the latter I have
>just committed a fix to CVS which will be in 3.3.1
good! alas, I've been using the former so I had to fix it by myself. 
now, it works fine.

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