Wave-Mechanical Treatment of the Li2 Molecule

Abstract

A treatment of the Li2 molecule by the Heitler-London method, with Slater wave functions for the atoms, has been carried out both with and without the customary approximations. In the absence of these approximations the binding computed is only a small fraction of that observed. It is found that the inner shells of the atoms may have an important effect on the magnitude of molecular binding, and may either increase or decrease it. Since their effect is associated with electron exchange it appears that they cannot be replaced by an equivalent potential field without serious error. Triple exchanges of electrons are found to be important, while polar binding is quite negligible in Li2. A criterion for the applicability of the ``interaction operator'' is developed; the error involved in its use with Li2 is small. A variational treatment has also been applied to this molecule. It yielded a binding energy less than that observed by about 0.5 e.v. The elimination of the residual error apparently requires the introduction of the interelectronic distances as coordinates. Convenient methods for the numerical treatment of multiple electron exchanges in complicated molecules are described.

Electronic Polarizabilities of the Alkali Atoms. II

“…37) with those implied by the present work. The value £ v a = 2.567 obtained here (see Table I 40 Finally the "intershell consistency term" yd~~ 2.508 appears to correspond directly to the effect first pointed out by the present author in Ref. 2 (see p. 1223), namely the shielding term £ C ore val produced by the dipole moment which is induced in the ion core by the induced dipole moment of the valence electron (2s).…”

The Electronic Structure of

“…(c) Consequent upon this, we find that the simple perturbation calculation is grievously in error; as we should expect, it gives much too high an energy and too large a nuclear separation. This is in excellent agreement with the work of Coolidge and James (12,13) on the lithium molecule and associated problems; these authors find that, in their case too, the perturbation method is inadequate to explain the bonding of Li 2 ; it looks therefore as though this method will have to be abandoned for all numerical work upon molecular structure.…”

On the nature of the two-positron bond: evidence for a novel bond type

“…This imposes the constraint of the orthogonalization of the valence sigma molecular orbital of Li 2 , composed mainly of the linear combination of the lithium 2s atomic orbitals, to the two core orbitals, composed mainly of the lithium 1s atomic orbitals, 52 yielding a nodal structure in the valence orbital. 59 The core-valence orbital orthogonalization and associated exchange interactions must be always taken into account in any realistic analysis of the alkali dimers, [53][54][55][56][57][58][59][105][106][107] or constructing any reliable core polarization potential. [60][61][62] Because of the distinguishability of electrons and positrons, this constraint and the relevant exchange interactions are absent in the case of the positronic orbital of (PsH) 2 .…”