Calculate Root-mean-square deviation (RMSD) of Two Molecules Using Rotation.

The root-mean-square deviation (RMSD) is calculated, using Kabsch
algorithm (1976) or Quaternion algorithm (1991) for rotation, between two
Cartesian coordinates in either .xyz or .pdb format, resulting in the minimal
RMSD.

WWW: https://github.com/charnley/rmsd