On the use of overllapping spheres in the SCF Xα scattered-wave method

doi:10.1016/0009-2614(73)80238-6

Chemical Physics Letters

Volume 23, Issue 2, 15 November 1973, Pages 149-154

https://doi.org/10.1016/0009-2614(73)80238-6 Get rights and content

Abstract

The use of overlapping spheres in the SCF Xα scattered-wave method is discussed. It leads to an improved description of both the ionization potentials and total energies of molecules where a substantial fraction of the charge due to the valence electrons is distributed over the interatomic region of constant potential. The effects of using improved exchange parameters for hydrogen-containing molecules are also considered. Results for ethylene, benzene, and carbon monoxide are reported.

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SCF-Xα-SW calculations for small molecules using the optimization technique of atomic-sphere radii
1992, Chemical Physics Letters
SCF-Xα-SW calculations of structure parameters, normal-stretching-vibration frequencies and ionization energies of the small molecules N₂, O₂, F₂, CO, CH₂ and NH₃ have been performed using the atomic-sphere radii determined by a technique previously proposed on the basis of optimization of the virial theorem and minimization of total energy. The effectiveness of this optimization technique in the SCF-Xα-SW method has been confirmed by the improved agreement between the calculations and experimental data for all the cases. An extension of this technique to more complicated molecules is discussed using the H₂CO molecule as a test example.
Structure électronique du complexe [(η5-C<inf>5</inf>H<inf>5</inf>)Fe(η6-biphényle)]+ et de ses états réduits
1991, Journal of Molecular Structure: THEOCHEM
Des calculs en méthode SCF-MS-X_a ont été effectués sur les complexes [CpFe(C₁₂H₁₀)]^x (x = +1, 0, −1). Ils indiquent que les deux plus bas niveaux vacants de l'espéce cationique à 18 électrons ont un caractère métallique important, à l'inverse de plusieurs autres complexes du type CpFe (polyaromatique)⁺. La réduction du cation correspond au peuplement de l'un ces niveaux à caractère métallique sans changement structural significatif. En particulier il est montré que, à l'inverse du complexe dinucléaire (CpFe)₂(biphényle), il ne peut exister de double liaison exocyclique dans l'espèce à 20 électrons en raison de l'inaccessibilité des orbitales π^∗ (biphényle ). Le rôle de l'interaction au second ordre entre les orbitales frontières des deux radicaux phényles est discuté.
SCF-MS-X_α calculations have been undertaken on the complexes [CpFe(C₁₂H₁₀)]^x (x= +1, 0, −1). It is found that, unlike the case of several other CpFe (polyaromatic)⁺ complexes, the two lowest unoccupied levels of the 18-electron cation show significant metallic character. Reduction of the cation leads to the occupation of one of these metallic levels without any significant structural change. It is shown that, unlike the case of the dinuclear Cp₂Fe₂(biphenyl) complex, an exocyclic double bond cannot exist in the 20-electron anion, because of the inaccessibility of the π^∗(biphenyl) orbitals. The role played by the second-order mixing between the frontier orbitais of the two phenyl rings is discussed.
Self-interaction corrected multiple-scattering X<inf>α</inf> method: Application to molecules
1991, Journal of Molecular Structure: THEOCHEM
The self-interaction correction (SIC) was introduced into the multiple-scattering X_α (MS-X_α) method, a powerful method for making calculations on large molecules containing heavy atoms. The self-interaction-corrected multiple-scattering X_α (SIC-MS-X_α) method was applied to three small molecules (ethylene, formaldehyde and ozone), two planar conjugated organic molecules (benzene and pyrazine) and two tetrahedral molecules (carbon tetrafluoride and carbon tetrachloride) to establish its efficiency. Ionization potentials and statistical energies were calculated and compared with those from the conventional MS-X_α and transition state MS-X_α methods. Ionization potentials obtained with the SIC-MS-X_α method agree well with those obtained from transition state calculations and with experimental values. The minimization of the total SIC energy with respect to the molecular orbital transformation is not important, because spherically averaged and volume averaged potentials are employed in the MS-X_α method with and without overlap. A single SCF procedure gives both the correct ionization potential and wavefunction of the system.
Electronic structure of γ′ phase containing Zr In nickel-base superalloy
1990, Solid State Communications
The electronic structure of γ′ phase in nickel-base superalloy containing impurity Zr is studied in the paper. Based on the model presented, we calculated the energy levels, the density of states, the partial-wave local density of states and the charge transfer of the system by use of the SCF-X_α-SW method. We compared the properties of Ni₆AlZr with those of Ni₆Al₂. The result shows that the nonbonding peaks decrease evidently, some new stable bonding orbitals appear in the lower energy region, the unoccupied orbitals move towards high energy region and the energy gap increases, which all indicate that the γ′ phase is intensified and is more stable after Zr instead of Al in the system. The result of charge transfer shows that the Zr atom loses outer electrons, which is of benefit for the Zr atom to dissolve in the γ′ phase.
Optimization of atomic sphere radii in the scattered-wave Xα method: A second look at the water molecule
1989, Chemical Physics Letters
A method for determining the atomic sphere radii which strongly influence the results in the scattered-wave Xα method is proposed on the basis of optimization of the virial theorem and total energy minimization. Molecular structure calculations are carried out on the water molecule. The minimum energy geometry has been found for a bond distance of 0.960 Å and bond angle of 106.2°, which are very close to the experimental values and have never been well-explained by previous SW-Xα calculations. Good agreement between calculated ionization energies and the force constant and experimental results show the effectiveness of the proposed method.
La<inf>0.7</inf>A'<inf>0.3</inf>MnO<inf>3</inf> catalysts by MS-Xα and CNDO/2 methods
1987, Journal of Electron Spectroscopy and Related Phenomena
This paper presents the orbital energies and the densities of states near the Fermi level of the pero Vskite type catalysts La_0.7A'_0.3MnO (A' = Sr, Ba, Ca), calculated by the MS-Xα method. It compares the frontier orbital electronegativities of the catalysts to those of the adsorbed molecules (O₂ and CO). This work also includes the total energy curves of the catalyst model with the adsorbed molecules calculated by the CNDO/2 method, compares the relative strength of adsorption of both O₂ and CO, and discusses the catalytic mechanism of the oxidation of CO.
It is promising that the noble-metal catalysts used in the oxidation of CO for purification of automobile exhausts and for other purposes could be replaced by the peroVskite type catalysts La_0.7A'_0.3MnO₃ (A' = Sr, Ba, Ca). The catalysts, which are very active in such an oxidation reaction, have been studied for years by many authors, and considerable headway has been made experimentally. Theoretically, however, interpretation of the catalytic mechanism in terms of molecular interactions has not been available. This paper presents some theoretical results of the adsorption and activity of the catalysts studied by the MS-Xα and CNDO/2 methods.

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^☆: Research sponsored by the Air Force Office of Scientific Research, United States Air Force (AFSC), under Contract No. F44620-69-C-0054.

¹: Permanent address: Lehrstahl für Theoretische Chemie der Technischen Universität München, D-8 München 2, West Germany.

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Chemical Physics Letters

Abstract

References (31)

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Intern. J. Mass Spectrom. Ion Phys.

Phys. Rev.

Phys. Rev.

Intern. J. Quantum Chem.

J. Chem. Phys.

Phys. Rev.

Cited by (164)

SCF-Xα-SW calculations for small molecules using the optimization technique of atomic-sphere radii

Structure électronique du complexe [(η<sup>5</sup>-C<inf>5</inf>H<inf>5</inf>)Fe(η<sup>6</sup>-biphényle)]<sup>+</sup> et de ses états réduits

Self-interaction corrected multiple-scattering X<inf>α</inf> method: Application to molecules

Electronic structure of γ′ phase containing Zr In nickel-base superalloy

Optimization of atomic sphere radii in the scattered-wave Xα method: A second look at the water molecule

La<inf>0.7</inf>A'<inf>0.3</inf>MnO<inf>3</inf> catalysts by MS-Xα and CNDO/2 methods

On the use of overllapping spheres in the SCF Xα scattered-wave method☆

Abstract

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Chem. Phys. Letters

Intern. J. Mass Spectrom. Ion Phys.

Phys. Rev.

Phys. Rev.

Intern. J. Quantum Chem.

J. Chem. Phys.

Phys. Rev.