scholarly journals Some Remarks on the Extended Hückel Approximation in the Independent-Electron MO Theory

1967 ◽  
Vol 40 (12) ◽  
pp. 2787-2792 ◽  
Author(s):  
Kenichi Fukui ◽  
Hiroshi Fujimoto
Keyword(s):  
Extended Hückel ◽  
Extended Hückel Approximation ◽  
Mo Theory

Qualitative Thinking in the Age of Modern Computational Chemistry, or What Lionel Salem Knows

2012 ◽  
Author(s):  
Roald Hoffmann
Keyword(s):  
Computational Chemistry ◽  
Emotional Reaction ◽  
Binding Energies ◽  
Complex Molecules ◽  
Computational Quantum Chemistry ◽  
Extended Hückel ◽  
Semiempirical Theory ◽  
Long Time ◽  
Inorganic Molecules ◽  
Extended Hückel Approximation

The achievements of modern computational chemistry are astounding. It is reasonable today to handle billions of configurations, and to achieve chemical accuracy, kilocalories say, in calculating binding energies and geometries, in ground and transition states of reasonably complex molecules. There is no question that the enterprise of computational theoretical chemistry is successful. Now Lionel Salem and I grew up and developed scientifically in the climate of the very same computer which made all this possible. Russ Pitzer taught me to punch cards; I still miss the sound of the key punch. The extended Hückel method, which several of us developed in the Lipscomb group, would have been impossible without modern computers. But I took a different turn, moving from being a calculator in the framework of semiempirical theory, to being an explainer, the builder of simple molecular orbital models. I was and am still doing calculations, but my abiding interest is in the construction of explanations. And also in thinking up moderately unreasonable things for experimentalists to try. In existing as a scientist, meaning that my work was of continuing interest to other chemists, I was helped in that I moved into whatever part of chemistry I did, just a little ahead of the heavy guns of computational chemistry. So I switched from organic to inorganic molecules just when organic molecules became reasonably calculable. Recently I’ve been less fortunate, for when I moved to solids and surfaces I came back into heavy fire—physicists had been doing calculations on these materials for a long time. And they were (are) hardly likely to believe that one-electron calculations and a chemical viewpoint are of value. I want to make some observations on computational quantum chemistry, perforce influenced by my prejudices. Given the advances in the field, any molecule I can calculate (without geometrical optimization), with the simplest extended Hückel approximation, can be done so much better by most computational chemists. So why don’t I feel threatened; why is there a role for people of my ilk? Or for Lionel. Actually, I do feel threatened and bypassed! But that’s just an emotional reaction, and my aging figures in it.

Benzene in the extended hückel approximation: an unexpected geometry

1972 ◽  
Vol 17 (3) ◽  
pp. 452-454 ◽  
Author(s):  
William L. Bloemer ◽  
Buddy L. Bruner
Keyword(s):  
Extended Hückel ◽  
Extended Hückel Approximation

Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

2019 ◽  
Author(s):  
Ishita Bhattacharjee ◽  
Debashree Ghosh ◽  
Ankan Paul
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Molecular Orbital ◽  
High Spin ◽  
Potential Energy Surfaces ◽  
Valence Bond ◽  
Deep Minimum ◽  
State Potential ◽  
Energy Surfaces ◽  
Mo Theory

The question of quadruple bonding in C<sub>2</sub> has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C<sub>2</sub>, N<sub>2</sub> and Be<sub>2</sub> and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the<sup> 2S+1</sup>Σ<sub>g/u</sub> (with 2S+1=1,3,5,7,9) states of C<sub>2</sub> and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N<sub>2</sub> and HC≡CH, the presence of a deep minimum in the <sup>7</sup>Σ state of C<sub>2</sub> and CN<sup>+</sup> suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

Qualitative MO theory of some ring and ladder polymers

1986 ◽  
Vol 90 (25) ◽  
pp. 6602-6610 ◽  
Author(s):  
John P. Lowe ◽  
Sherif A. Kafafi ◽  
John P. LaFemina
Keyword(s):  
Ladder Polymers ◽  
Mo Theory

Role of population analysis in LCAO-MO theory of transition-metal clusters

1975 ◽  
Vol 25 (11) ◽  
pp. 1201-1207 ◽  
Author(s):  
J. Málek ◽  
R. A. Evarestov ◽  
A. N. Ermoshkin ◽  
B. Hejda ◽  
K. Polák
Keyword(s):  
Transition Metal ◽  
Metal Clusters ◽  
Population Analysis ◽  
Transition Metal Clusters ◽  
Lcao Mo Theory ◽  
Lcao Mo ◽  
Mo Theory
Sign in / Sign up

Export Citation Format

Share Document