Louis Chopin Cusachs

Semiempirical Molecular Orbitals for General Polyatomic Molecules. II. One‐Electron Model Prediction of the H–O–H Angle

A consistent one‐electron semiempirical molecular orbital method based on the approximation Hij=Sij(2−| Sij |)(Hii+Hjj)/2 has been used with atomic data to predict the equilibrium geometry of the water molecule. A variety of plausible parameters predict an equilibrium H–O–H angle in the range 95°—105°. Success and limitations of the method are attributed to the fidelity with which it reproduces important one‐electron effects. In less critical cases, this model resembles the Wolfsberg—Helmholz and other non‐Huckel semiempirical MO treatments.

Selection of Molecular Matrix Elements from Atomic Data

A simple internally consistent recipe for obtaining atomic orbital matrix elements (Hii) from atomic spectral data agrees with values obtained from empirical molecular ionization potentials via molecular orbital calculation. Regularities observed lead to very simple expressions useful for adjustment of parameters for charge transfer. Various assumed relations between atomic valence‐state quantities and orbital matrix elements are compared with the observed data for selected atoms. In the cases studied, valence‐state ionization potentials depend quadratically on the degree of ionization, but can be satisfactorily approximated by linear functions for net charges between −1 and +1. In the linear approximation, the second term is the same for both occupancies of both s and p orbitals.

Selection of Molecular Matrix Elements from Atomic Data. III. 3d, 4s, and 4p Orbitals for Na, Mg, Al, Si, P, S, and Cl

A modification of the method of Cusachs and Reynolds has been used to derive valence‐state ionization potentials for the 3d, 4s, and 4p orbitals of third‐row elements. For a fixed ionic charge, these VSIP are found to vary linearly with atomic number.

LCAO-MO Formulation of Pseudopotential Theory

Abstract Pseudopotential Theory replaces the requirement that valence orbitals be orthogonal to core ones by an effective potential in the computation of the valence orbitals. Instead of the usual differential equation or perturbation treatments, the appropriate secular equation for the expansion of the valence molecular orbitals in a nonorthogonal atomic orbital basis is obtained. It takes the famillar form with the diagonal elements of the energy matrix significantly modified and with corrections to the overlap matrix and off-diagonal energy matrix elements that may normally be disregarded in semiempirical molecular orbital calculations.

Effects of Charge Separation in a Hetronuclear Molecule: I, Changes in H11 Due To Neighboring Charge

Abstract Ionization energies are commonly used to estimate atomic orbital matrix elements (H11′s) used in semiempirical molecular orbital calculations, but no adequate method is available to predict the change in atomic ionization energies resulting from charges on neighboring atoms. Using as a model the one-electron nuclear attraction integral, this paper develops a function to predict the effective potential produced by neighboring charges. The potential function is of the form

The 4d, 5s, and 5p Orbitals of Rhodium

Abstract The 4d, 5s, and 5p orbitals of rhodium have been studied by semiempirical molecular orbital calculations for a Rh2 molecule. Overlap populations, overlap energy, and orbital energies were computed as functions of the orbital exponents of Slater type atomic orbitals. This study was prompted by extremely unsatisfactory results obtained attempting to predict electronic spectra, structure, and bonding in a number of rhodium complexes using analytic atomic orbitals deduced1 from accurate Hartree-Pock(HF) atomic calculations. “These reference calculations considered only the atomic configuration (4d)7(5s)2 for rhodium.