25 Method B: Richard's solution to problem of unequal atoms

• Position the dividing plane between atoms in proportion to known atom radii.
• Place dividing plane farther from large atom according to the following formula:

          R
   S =  ----- D  which is the same as  R s = S r
        R + r

  where R is radius of the large atom and S is distance of the plane from the large atom, r and s are the analogous quantities for the small atom, and D=s+S.
• Vertices of polyhedra now are no longer at center of sphere formed by 4 atoms.