deal with reduced dof from frozen atoms

[js850]

We should have the capability to deal with a cluster with frozen atoms

1 frozen atoms:

• no translational symmetry
• reflection only through the frozen atom
• rotation only around the frozen atom

2 frozen atoms:

• rotational and reflection only around (through) the line between them

3 frozen atoms:

• no rotational symmetry
• reflection symmetry through the plane of the frozen atoms

4 or more frozen atoms:

• no symmetry except permutational

Of course if you have three atoms on a line then you have the symmetries of a 2 frozen atom system, etc.

In particular this means:

• rotation around points not at the origin, and around lines
• reflection through points not at the origin, through lines, and through planes