Abstract
<jats:p>Within the framework of the Heitler–London model applied to the hydrogen molecule in its ground state, the contributions to the binding energy from three types of interactions are compared: electron–electron interaction including exchange, internuclear interaction, and the interaction of each electron with the neighboring nucleus. It is shown that, in the first order of perturbation theory, the exchange interaction gives a positive contribution, which corresponds to mutual repulsion rather than the expected attraction. This is because the ground-state wave function of the atom does not change sign. Thus, the attraction between atoms in the first order is due only to the interaction of each electron with the neighboring nucleus. In addition, a coordinate transformation is found that makes it possible to obtain analytical expressions for the normalization coefficient of the two-electron wave function, which allows saving computational time.</jats:p>