The second‐order energy contribution from the spin–orbit interaction operator to the potential energy curve of Cr₂

The second‐order Rayleigh–Schrödinger energy correction to the Born–Oppenheimer potential energy due to the spin–orbit interaction can be expressed as a linear response function evaluated at zero frequency. We have calculated this energy contribution to the Cr₂ singlet ground state X¹ Σ⁺_g potential energy function for a multiconfiguration self‐consistent field (MCSCF) wave function. The calculations show that the effect of spin–orbit interaction is small and of the same magnitude for the whole potential energy curve.