Accurately solving the electronic Schrِdinger equation of atoms and molecules using explicitly correlated (r12-)MR-CI: the ground state potential energy curve of N2

The recently proposed MR-CI ansatz which contains terms linear in the interelectronic distances (r12) is used to compute the potential energy curve of N2 by means of r12-MR-ACPF. The computed spectroscopic constants with the respective errors, e.g. ΔDe (−0.2 kcal/mol), ΔRe (+1×10−4 Å) and Δωe (+2 cm−1), are found to be in excellent agreement with values derived from experimental spectra. With only a moderate computational effort, we reach accuracies which are probably out of reach of present day (traditional) CI-methods and computers.