Ab initio study of helium dimer

The interaction of the helium dimer system has been studied by means of a newly developed ab initio approach in the framework of the modern valence bond (VB) theory. The self consistent field for molecular interactions (SCF-MI) wave function is used as reference state for a multistructure VB calculation. The electron correlation contributions are evaluated by a strategy based on the optimization of the virtual space of the VB wave function. The resulting wave function, while very compact, provides results of quality comparable to that of the most accurate calculations realized on this system. The well depth of the interaction potential is found to be 33.7 μEh. The calculated potential is consistent with the existence of a bound vibrational state