Ab initio study of helium dimer

The interaction of the helium dimer system has been studied by means of a n ewly developed ab initio approach in the framework of the modem valence bon d (VB) theory. The self consistent field for molecular interactions (SCF-MI ) wave function is used as reference state for a multistructure VB calculat ion. The electron correlation contributions are evaluated by a strategy bas ed on the optimization of the virtual space of the VB wave function. The re sulting wave function, while very compact, provides results of quality comp arable to that of the most accurate calculations realized on this system. T he well depth of the interaction potential is found to be 33.7 muE(h). The calculated potential is consistent with the existence of a bound vibrationa l state. (C) 2001 Elsevier Science B.V. All fights reserved.