Intermolecular potentials calculated by an extended geminal model: Theory

A model aimed at describing intermolecular interactions is formulated within the context of extended geminal models. The model has the following properties: It has a conceptual structure which facilitates interpretation. The model can be applied for any intersystem distances. The model is size extensive. Basis set superposition errors can be practically eliminated. The model is computationally efficient. A test calculation on the helium dimer yields a well depth of 10.64 K. The experimental determined value of the well depth is (10.79±0.22) K.