Avoid bond angles of 0 or 180 degrees. Use a dummy atom at a location orthogonal to the co-linear triple and define angles w.r.t. the dummy atom.
Be aware that bond angles can be explicit - these are easily recognized - but also implicit, in the definition of dihedral angles: it is absolutely imperative that such implicit bond angles are never 0 or 180 degrees: the dihedral angle will not be properly defined and an error will occur.
The program may in some cases be able to recover from 0/180 degree bond angles, but this is not a certainty. If it fails, the geometry update steps may go completely wild. Even worse: the steps may remain small but convergence is not reached, without a clear and explicit indication in the output about the cause.
