On the electronic structure of Li2 (X1) and its changes with internuclear distance

Abstract

A compact, yet accurate, and strictly virial-compliant ab initio electronic wavefunction for ground-state Li 2 is exploited for a study of the molecule's electronic structure and electron density. Symmetry-breaking problems that emerge at the single-configuration level are solved in a multiconfigurational spin-coupled approach that enables simultaneous optimization of angularly correlated "resonating" configurations. Particular emphasis is placed on the accurate determination of the electron density's bifurcation points and of the quadrupole moment as a function of internuclear distance R. Tentative connections are drawn between the R dependence of the electron density's topological structure and quadrupole moment and that of the electronic wavefunction. Computation of the latter constitutes the first application to systems other than isolated atoms of the optimized basis set generalized multiconfiguration spin-coupled method, which entails use of nonorthogonal orbitals and Slater-type basis functions with variationally optimized exponential parameters.

Nonnuclear Attractors in Heteronuclear Diatomic Systems

“…For instance, LiNa shows a maximum in the zz component of Θ at a bond length of 3.7 Å, almost at the same point that is associated with the upper limit for NNM occurrence (3.64 Å) . In addition, Li 2 exhibits a similar maximum nearly where one NNA splits in two …”

“…17 In addition, Li 2 exhibits a similar maximum nearly where one NNA splits in two. 36 The other homonuclear diatomic molecules studied here customarily present a maximum or minimum in Θ zz that occurs approximately at the same points where NNMs appear/ disappear or also when the number of these nonnuclear maxima changes. For instance, this is noticed for second-row diatomics except perhaps for Be 2 , in which case the electronic structure treatment should be improved for a definitive answer.…”

Local Spin Analysis and Chemical Bonding

“…Dilithium is an apparently simple six‐electron system that has received some attention in the past 44–46. In the simplest MO picture the electron configuration of the valence electrons is ${2{\rm{{\rm \sigma} }}_{\rm{g}}^{\rm{2}} }$ , which is consistent with a perfect pairing of the electrons and a formal bond order of 1.…”

“…In the simplest MO picture the electron configuration of the valence electrons is ${2{\rm{{\rm \sigma} }}_{\rm{g}}^{\rm{2}} }$ , which is consistent with a perfect pairing of the electrons and a formal bond order of 1. It has been argued46 that the ${{}^1\Sigma _{\rm{g}}^ + }$ ground state requires a correlated wave function for its proper description. As shown in Table 2, the number of unpaired electrons on each Li atom is 0.37, with a minor contribution of the π orbitals.…”

Electronic structure of BeH2

“…The inherent qualitative description of the electronic structure is reminiscent of results obtained for Li 2 28 and BH 3 18, a fact that suggests it may be common to other highly symmetric molecules.…”