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Chlorine - chlorine interactions are too strong.
This shows up in hexachlorobenzene crystal and in crystalline Cl2. The fault has
been traced to the diffuse "d" orbitals on chlorine.
These orbitals are important in transition states and hypervalent compounds. In
most systems, they are not important, but when a diffuse "d" orbital interacts
with another similar
orbital, the interaction is unusually large. This results in extra
stabilization, as shown in the heats of
sublimation.
Silver - silver interactions are inaccurate. There are few reference data on silver compounds. If more were available, this fault could be corrected.