This paper presents an interpretation of the chemical binding found in the first-row homonuclear diatomic molecules. The interpretation is based upon the one-electron density distribution and the forces which it exerts on the nuclei. The general topographical features of the density distributions are discussed in relation to ``molecular size'' and the manner in which the total charge is partitioned between different spatial regions. The binding in these molecules is discussed in terms of the density difference distributions which picture the redistribution of charge which results from the formation of the molecule. It is proposed that the density difference distribution, or Δρ map, may be taken as the pictorial representation of the ``bond density.'' The forces exerted on the nuclei in the molecule are related to the changes in the charge distribution pictured in the ``bond density'' and a quantitative discussion of the manner in which electrostatic equilibrium is attained to give a stable molecule is given in terms of the forces. The concepts of bonding and antibonding are compared with the terms binding and antibinding, terms which are defined in terms of the forces exerted on the nuclei. In particular, both vertical and adiabatic ionization processes are viewed from the standpoint of the change in the electronic force contribution between the molecule and the molecule ion. A definition of ionic and covalent binding based on the density difference distributions is presented. The Δρ map (or bond density) for covalent binding is shown to be characterized by a density increase located between the nuclei and shared equally by each. The Δρ map for ionic binding exhibits an increase in charge density which is localized on a single nucleus. A partitioning of the total electronic force in accordance with the Δρ maps demonstrates that in covalent binding, the nuclei are bound by the density which is shared between them, while in ionic binding the nuclei are bound by the density which is localized on a single nucleus.

Articles you may be interested inTheoretical Compton profile anisotropies in molecules and solids. IX. Chemical bonding and 0-90 anisotropies in the firstrow diatomic hydrides AH J. Chem. Phys. 79, 2913 (1983); 10.1063/1.446113 Study of the electronic structure of molecules. XXII. Correlation energy corrections as a functional of the HartreeFock type density and its application to the homonuclear diatomic molecules of the second row atoms J. Chem. Phys. 60, 1288 (1974); 10.1063/1.1681193Study of the electronic structure of molecules. XXI. Correlation energy corrections as a functional of the HartreeFock density and its application to the hydrides of the second row atoms Hartree-Fock wavefunctions are presented for the LiH(X 12;+), BeH(X 22;+) BH(X 12;+) CH(X 2II ) NH(.~32;-), C?H(X2IIi), and H~(Xl2;+) molecules. These are the analytic 'self-consiste~t-field wa~e~ funct~ons obtamed from the sol~tJons of the Hartree-Fock-Roothaan equations. Large sets of Slater-;type functions centered on bot~ nuclel were used as the expansion basis, and extensive optimization of the orbital exponents has been carned out. The ~otal energies obtained for R.(exptl) are -7.98731, -15.15312, -~5.13~37, -38.27935, -54.9?8~6, :-,5.42083,. and -100.07030 hartrees, respectively, for the AH hy-d=ldes hsted above. The first lOmzation potentials, which are obtained from the Hartree-Fock energy differe~c.es between.AH and AH+ systems,. are 7. 02, 8.14, 8.45,10.08,12.82,11.44, and 14.54 eV, respectively. In addltl~n, potential curves, ~pectroscoplC constants, and c~rtain other energetic quantities are presented. C:u~e estlmat~s of the co;relatlo.n energy of the first-row hydndes are made and such quantities are compared wlthm t~e senes ~nd wlth thelr respecti:ve united and separated atoms. These results suggest that the changes m correlatlOn energy of AH relative to the correct united atom is independent of which hydride is involved and the change is small.

A partitioning of the total molecular charge distribution between the nuclei in a molecule is proposed. The method may be termed a "natural partitioning," as it is suggested by the nature of the charge distribution itself; the point along the internuclear axis at which the charge density attains its minimum value between a pair of bonded nuclei defines the position of the partitioning surface. The resulting populations are further divided into nonbonded and bonded populations for a terminal nucleus and into two bonded populations for a nucleus with two adjacent nuclei. These charge populations together with their associated nonbonded and bonded radii are sufficient to classify and characterize a molecular charge distribution. The variations in these parameters serve to summarize in a concise manner the type and variation in the type of bonding through isoelectronic series of molecules and through series of oxides, fluorides, etc., in ground, excited or charged states. A corresponding partitioning of molecular properties is illustrated in terms of the dipole moment, and the general inadequacy of this moment in providing a measure of the charge transfer within a system is discussed. Finally, the transferability of these bonded and nonbonded populations between different bonding environments (a necessary condition for the transferability of molecular properties) is illustrated and discussed. (1) (a) McMaster University; (b) University of Massachusetts.(2) (a) L. Pauling, "The Nature of the Chemical Bond," 3rd ed,

No abstract

The calculation of the electronic structure of atomic and molecular systems involves the determination of a number of integrals over the electronic coordinates. These calculations are feasible only by the use of high-speed, large-memory digital computers. This discussion is based on a culmination of experience obtained in this laboratory with regard to methods useful in the evaluation of two-center integrals by means of digital computers. The ground work for this paper, in terms of the analysis employed, is given in a series of papers by Roothaan, Ruedenberg, and Jaunzemis, but significant changes have evolved which offer considerable improvements and more economical calculations. The analysis presented here is especially the result of efforts to take full advantage of the capabilities of present digital computers. The methods advocated here are thought to be near optimal to a completely reliable and automatic computation of the electronic integrals in question with the desired accuracy. A not insignificant aspect of the methods given here is that an approach was sought which is unfailingly reliable and accurate regardless of the AO's involved in the integrals and at the same time as economical as possible.