The "sextuple" bond of Cr₂

Using a self-consistent 6000-configuration wave function corresponding to spin-optimized generalized valence bond (GVB) plus interpair correlations and van der Waals interactions, we find that the ground state of Cr₂ is best described not as a sextuple bond, but rather as an antiferromagnetic dimer with very low-lying electronic excited states. Our calculations predict a red shift of 0.3₀ eV for the first strong absorption in Cr₂ as compared with Cr, in excellent agreement with matrix isolation studies. The ground state is calculated to have R_e = 3.O6 Å and D_e = 0.3₅ eV. The best experimental dissociation energy is 1.0 ±0.3 eV (based on our structural parameters) but may suffer from experimental difficulties.