Ground state of the Mo2, W2 and MoCr molecules: a second and third order multireference perturbation theory study

The potential energy curves of the molecules Mo2, W2, and CrMo have been studied ab initio using large basis sets and the “n-electron valence state perturbation theory” up to the third order in the energy. The third order results for Mo2 and W2 reproduce the equilibrium distances r_e and the harmonic frequencies omega_e in fairly good accordance with the experimental values but tend to underestimate the dissociation energy. The CrMo molecule, for which experimental dissociation energy data do not exist yet, is predicted to have a value for D_e of ~2.5 eV.