GEOM - PLANES

PLANES


Computes mean planes of groups of up to 20 atoms. The program prompts the user to type the atom labels, and asks whether the atoms are to be weighted according to the precision of their postions or whether unit weights are required. There follows a prompt for the option to include in the mean plane atoms related by a center of symmetry at the crystallographic origin, in which case only the atoms in the asymmetric unit need to be specified. In groups with any other symmetry, all equivalent positions of the atoms must be present in the model file and explicitly referenced in the groups contents.

Also, all atoms in a group must be in the same asymmetric unit, since no symmetry transformations or lattice translations are applied. The mean plane is defined as the plane at right angles to the groups axis of highest moment of inertia, which is the eigenvector of the tensor of inertia. The weighted sum of squared deviations of the atoms from the plane is minimised.

If only two atom labels are given, the angle between the line so defined and all other lines and plane normals are calculated.