Here is a patch to Openbabel’s stable tarball source code 2.1.1
It has an added flag to OBAtom OBFixed which means that the atom will
remaini fixed
during OBForceField operations.
It also includes some checks for nan values in the torsion energy
calculations as
it was causing some molecules with loops to “explode” after a period of
stability.
For those who develop Openbabel, it would be nice if you added these to
Openbabel itself.
For those who develop Avogadro, the AutoOpt tool that I have been working on
needs this patch to be in Openbabel to function properly, but there is a
#define which can be commented out to allow it to function without the
patch.
Cheers,
Ross Braithwaite