BROKEN BOTTLENECKS AND THE FUTURE OF MOLECULAR QUANTUM MECHANICS.

doi:10.1073/PNAS.45.3.394

Paper

BROKEN BOTTLENECKS AND THE FUTURE OF MOLECULAR QUANTUM MECHANICS.

Published Mar 1, 1959 · Broken Bottlenecks, C. Roothaan

Proceedings of the National Academy of Sciences of the United States of America

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Abstract

Dirac once stated that, in principle, the whole of chemistry is implicit in the laws of quantum mechanics.1 In other words, quantum mechanics offers the possibility that all quantities of chemical interest-the sizes, shapes, and energies of molecules in their ground states and in activated states, and their electric, magnetic, and thermodynamic properties-may eventually be computed purely theoretically. A similar statement applies to the physics and chemistry of solids and liquids. The present situation for the application of quantum mechanics may be compared with that for the application of the principles of classical mechanics in the years following the discovery of Newton's laws of motion. It took many years for the discovery by Lagrange, Hamilton, and others of the most effective mathematical formulations of Newton's laws. After that, very great and continuing efforts have proved necessary and worth while in using these laws to solve the innumerable physical, astronomical, and engineering problems to which they are relevant. A similar history seems likely, but at an accelerated pace, for the future application of quantum mechanics to chemistry and molecular and solid-state physics. Satellites and space ships will make full use of both classical and quantum mechanics. There is one factor which tends to obscure the inherently great possibilities for the quantitative application of quantum mechanics to chemical problems. Namely, the activities of tens of thousands of chemists during the last hundred and more years have created an immense body of empirical knowledge, most of which was rather well organized when quantum mechanics arrived in 1925-1926. Quantum mechanics has shown itself extremely fruitful for a qualitative theoretical explanation of, for instance, the empirical rules of valence. But until very recently it has for the most part been less successful in quantitative predictions. We think there are two reasons for this. Namely, first, the answers to the easy problems had already been obtained in the laboratory so that there was no need to ask quantum mechanics to provide them. Second, it so happens that the more difficult problems of chemistry and molecular physics are of a high order of complexity in terms of the mathematical analysis and the computational efforts required for quantitative results. However, and this is the point of our paper, those who are working in this field are now catching up, and we believe that the results of theoretical computations are going to compete more and more strongly with experiment from now on. The present paper deals primarily with quantum-mechanical calculations in the field of molecular electronic structure and chemical valence, but the methods and results should be widely applicable also to solid-state physics and other fields. To understand the present situation better, it will be helpful to look back to the early days of quantum mechanics. For the first few years many of the world's best

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Quantum mechanics has the potential to revolutionize chemistry and molecular physics, with its theoretical predictions increasingly competing with experiment in molecular electronic structure and chemical valence.

PopulationOlder adults (50-71 years)

Sample size24

MethodsObservational

OutcomesBody Mass Index projections

ResultsSocial networks mitigate obesity in older groups.

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BROKEN BOTTLENECKS AND THE FUTURE OF MOLECULAR QUANTUM MECHANICS.

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References

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