MR-ccCA: A route for accurate ground and excited state potential energy curves and spectroscopic properties for third-row diatomic molecules

The potential energy curves for diatomic molecules containing third-row elements were examined using the multi-reference correlation consistent composite approach (MR-ccCA) to determine the applicability of the new approach for these systems. Remarkably smooth potential energy curves resulted, though the methodology was not designed, per se, for potential energy curves, particularly due to the additive nature of the methodology. A number of properties have been considered including the dissociation energy Do, well depth De, equilibrium bond length re, vibrational constants (ωe, ωexe) and rotational constants (Be, αe) and these properties have been compared with the experimental values for the ground state diatomics. Additionally, potential energy curves and spectroscopic properties of several of the lowest excited states of As2 have been determined, with the addition of transition energies Te and the determinations have been compared to experimental and theoretical values.