Hello,

I have probably stupid questions concerning the output of aoforce and numforce:

1.) Both programs write the Cartesian force constant matrix, which is the Hessian matrix. I have calculated the eigenvectors of this matrix which should be the normal mode vectors. However, these eigenvectors are NOT identical to the normal modes written in the output of aoforce/numforce. Why? What do I have to calculate to get from the force constant matrix given in the output to the normal modes given in the output?

2.) Is the Hessian matrix mass-weighted? (As far as I understand it is not.)

3.) It is written in the output that one has to divide the given normal modes by sqrt(reduced mass * 1822.88853) to get mass-weighted normal coordinates. However an eigenvector is never unique and if one multiplies the whole vector with a certain number it is still an eigenvector of the same matrix. (The factor is lost when normalizing to unity again.) I do not understand this point as well.

VS