Schrodinger: Difference between revisions

=== Extending Schrodinger's Theory ===

In 1926, Fritz London had become aware of Schrodinger's papers. Following Sommerfeld's encouragement and support, he received a grant from the Rockefeller Foundation to work in Zurich with Schrodinger. London arrived in Zurich early in April 1927, when Schrodinger was in the USA. In Zurich, London met Walter Heitler. Just like London, Heitler was also very keen to learn more about Schrodinger's paper and transferred his grant to Zurich.

However, Schrodinger's style was to carry out research on his own. In contrast to Sommerfeld and Born, who ran large research groups, Schrodinger was not interested in supervising the research of students or postdoctoral fellows. Almost as soon as Schrodinger returned to Zurich, Schrodinger was making the arrangements to go to Berlin. Both London and Heitler, finding themselves unsupervised in Zurich, decided instead to collaborate together on extending Schrodinger's theory.

They chose a key problem in chemistry : the bonding of the hydrogen molecule. They wrote down an approximate form for the wave function of this two-electron system in terms of a product of the hydrogen atom wave functions (orbitals) for the electron centered on each atom. This "valence bond" form of the wave function gave some electron density in the region between the two atoms to produce a chemical bond. After some non-trivial calculations, they were able to compute the strength of this chemical bond.

This work was submitted for publication almost exactly one year after the submission of Schrodinger's first paper on wave mechanics. It was the first advance in applying Schrodinger's quantum mechanics to a molecule with more than one electron. It remains a major paper in quantum chemistry.

This work also illustrates well how the application of Schrodinger's theory to molecules with more than one electron, which is what made him so famous to the wide scientific world. It was done by others, and not by Schrodinger himself. He was aware of this important developments and took Fritz London as an assistant when he moved from Zurich to Berlin. Later, he also arranged for Heitler to join his Institute for Advanced Studies in Dublin in 1941, where he eventually took over from Schrodinger as Director. Heitler took up Irish citizenship and was elected a Fellow of the Royal Society.

When Fritz London took his Rockefeller grant to Berlin with Schrodinger, he found the appointment surprisingly congenial. He discovered that Schrodinger's attitude of not interfering with his research had the big advantage that he could work independently. London's work with Heitler on chemical bonding was becoming well known. They had received major compliments on it from no less than Heisenberg, von Laue and Born. Taking quantum mechanics beyond the hydrogen molecule proved difficult at that time because of the computations involved. Meanwhile, London found he could simplify the calculations using the powerful methods of group theory. This work became influential.

London also applied a perturbation theory approach to Schrodinger's wave functions to provide a theoretical framework for the long-range dispersion forces between atoms. These "London forces" are significant for the properties of liquids and gases and even for the structures taken up by biological molecules.

Tempting offers to Fritz London came from Born in Gottingen and Sommerfeld in Munich, but he preferred the dynamic scientific scene then prevalent in Berlin, which was at its peak in the late 1920s. He much enjoyed the seminars where the highly promising younger members like himself, Viktor Wisskopf, Max Delbruck, Eugene Wigner and Leo Szilard could present their latest ideas to the great senior physicists present, including Planck, Einstein, Schrodinger, von Laue, and Nernst. With quantum mechanics starting to influence chemistry, researchers such as Michael Polanyi, Lise Meitner and Otto Hahn would also come over from the Kaiser Wilhelm Institute for Chemistry. Afte the seminar, the participants would often adjourn to a local tavern to continue the discussions. Sometimes, the Schrodingers would invite the group back to their apartment for Viennese sausage parties.

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"Berlin was the most wonderful and absolutely unique atmosphere for all the scientists. They knew it all and they appreciated it all. One had a bit forgotten the first war, and before the second, so it was absolutely a wonderful time. The theatre was at the height, the music was at the height, and science with all the scientific institutes, the industry. And the most famous colloquium, the Berlin Academy had published lectures which were very famous too. There were lots of friends who came together, not on a special day. It was absolutely a very social life. My husband like it very much indeed. "

- Anne Schrodinger

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Another young scientist who came to Zurich to work with Schrodinger was the American Linus Pauling. He had won a Guggenheim grant, which enabled him to come to Europe to learn about the new ideas in quantum mechanics in several centres. He stopped off in Munich to see Sommerfeld, visited Born in Gottingen, and then went to Zurich to learn wave mechanics.

Like Heitler and London, Pauling found Schrodinger elusive in Zurich. But he immediately realised the potential of the work of Heitler and London regarding chemical bond. As a chemist, he could see how the Heitler-London valence bond theory could be extended to calculate the structure and properties of many important molecules -- including those of interest in organic chemistry --. In due course, he used this theory to explain the tetrahedral shape of the methane molecule and the strong bonding in aromatic molecules like benzene. His book, "The Nature of the Chemical Bond", brought this research together. Later, he was awarded the Nobel Prize for Chemistry in 1954. Years later, Pauling was also involved with movements to stop nuclear testing. In 1962, he was awarded a second Nobel Prize, this time for Peace.