Hi there,

in case someone is curious about the commits I just checked in. Apart from some 
cleanup and some better logging output, I changed the internal handling of 
angle constraints:

Planar and and torsion angles used to be handled internally by their cosine. 
This had caused a problem for angles of 0 or 180 degree, where the derivative 
of the constraint would become zero and the constraint could not be enforced 
correctly. Specifically, this caused problems for planar benzene molecules that 
I tried to constrain.

With my change, the constraints are now internally handled as angle, the 
torsion angle as signed angle. It works beautifully for my test case. I 
adjusted the metadynamics code, otherwise, no code seems to be affected.

For the user, there should be no difference except in the case that someone 
would have explicitly specified torsion angles with incorrect sign in the input 
file. I doubt that anyone would do that...

Greetings,
Norbert
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