The lattice energy calculations with the Williams 01 potential were calculated with a version of Neighcrys with an atom typing bug. Page 186 col 2 paragraph beginning "Lattice energy calculations" should read

gives the intermolecular lattice energy as -134.7 kJ mol

^{-1}(instead of -133.0) forIand -133.5 kJ mol_{R}^{-1}(instead of -131.9) forII._{O}

Since the energy shift is small and almost constant the conclusions are unaffected.