The recent developments of ab initio methodology have been successful in yielding the complete rotational-vibrational spectrum of near-spectroscopic accuracy for the diatomic molecules B2, F2 and O2. Most significantly, this theoretical work provided the spectroscopic data which, as yet, has been inaccessible to experimental spectroscopy for the boron and oxygen molecules in their ground states. In particular, for the ground state of O2, the theoretical studies yielded 15% of the full spectrum which has eluded the spectroscopic measurements. For the ground state of B2, the theory has yielded 85% of the full spectrum which could not be determined experimentally. Furthermore, the theoretical results led to the reassignment of the electronic transitions in B2 that are believed to be responsible for the observed spectrum reported by Bredohl and co-workers. Ab initio potential for the ground state of F2 has yielded the rotational-vibrational spectrum within 5 cm-1 of the experiment and predicted an additional vibrational energy level. The theoretical results are based on the ability of the newly developed ab initio method (on the basis of intrinsic scaling) to approximate the full configuration interaction (FCI) and complete basis set (CBS) limit very closely. Furthermore, the effects that are due to the inner shell (core) electron correlation and relativity have been found to be significant.
In addition, some new developments of ab initio methodology for application to larger systems are also discussed.