Can anyone suggest some free software for calculating the principal axes for a protein 3d structure? Ideally the input will be the PDB file of 3d coordinates, and the program will return the moment of inertia tensor and the principal axes. I DON'T want the molecule to orient further along the principal axes.

There are a few examples of codes available in the net, but it would be good if someone knows about a well known software to do this job.

Thanks in advance

great!!! many thanks