The performance of multiconfigurational second order perturbation theory has been analyzed for the description of the bonding in CuH, Cu2, NiH, and Ni2. Large basis sets based on atomic natural orbitals (ANOS) were employed. The effects of enlarging the active space and including the core‐valence correlation contributions have also been analyzed. Spectroscopic constants have been computed for the corresponding ground state. The Ni2 molecule has been found to have a 0+g ground state with a computed dissociation energy of 2.10 eV, exp. 2.09 eV, and a bond distance of 2.23 Å. The dipole moments of NiH and CuH are computed to be 2.34 (exp. 2.4±0.1) and 2.66 D, respectively.... [Leer más...]