Nicolas SAPAY wrote:
Hello everybody,

I've got an awful doubt on how the Urey-Bradley (UB) term is taken into
account in the potential energy. When an angle has got regular and UB
parameters, how this will appear in the .edr file?

If you have a force field with both angle function 1 and angle function 5 (IIRC, for U-B) defined for the same set of 3 atoms, then to the best of my knowledge, GROMACS will do both blithely and the output will go into "Angles" and "U-B" in the expected fashion. Certainly this happens when such functions are defined for different sets of 3 atoms. Note that from GROMACS point of view, the U-B term includes both the angle stretch and the harmonic position stretch. CHARMM the program lists only the latter as U-B.

The angle energy will
only appear in the UB term only or it will be splitted between Angle and
UB terms? I guess that both parameters are used in the computation but I'm
not sure whether they are added before be printed in the .edr file or not.

I'm not quite sure what you're asking, but the structure of the bonded interaction code is such that all of the angle functions of type 1 will contribute only to "Angles" and all of the angle functions of type 5 will contribute only to "U-B".

Mark
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