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Walter Kohn

Walter Kohn (born March 9,1923 in Vienna, Austria) is an Austrian-born American theoretical physicist. He was awarded, with John Pople, the Nobel Prize in chemistry in 1998. The award recognized their contributions to the understandings of the electronic properties of materials. In particular, Kohn played the leading role in the development of the density functional theory, which made it possible to incorporate quantum mechanical effects in the electronic density (rather than through its many-body wavefunction). This computational simplification led to many insights and became an essential tool for electronic materials, atomic and molecular structure.

Early years in Canada

Kohn arrived to England as part of the famous Kindertransport rescue operation. because he was a German national, he was sent to Canada by the English, as a 17 year old, immediately after the annexation of Austria by Hitler. In July 1940, the young Kohn traveled as part of a British convoy moving through U-boat-infested waters, to Quebec City in Canada; and from there, by train, to a camp in Trois Rivieres. He was at first held in detention in a camp near Sherbrooke, Quebec. This camp as well as other camps provided a modicum of educational facilities that Kohn used to the fullest, and he finally succeeded in entering the University of Toronto. As a German national, the future Nobel laureate in chemistry was not allowed to enter the chemistry building, and so he opted for physics and mathematics. A short but fascinating autobiography may be found in the Nobelist webpage.

Scientific career

Kohn received a war-time bachelor's degree in applied mathematics at the end of his one-year army service, having completed only 2 1/2 out of the 4-year undergraduate program, from the University of Toronto in 1945; he was awarded an M.A. degree in applied mathematics by Toronto in 1946. Kohn was awarded a Ph.D. degree in physics by Harvard University in 1948, where he worked under Julian Schwinger on the three-body scattering problem. At Harvard he had also fallen under the influence of Van Vleck and solid state physics.

He moved from Harvard to Carnegie Mellon University from 1950-1960, after a short stint in Copenhagen as a National Research Council of Canada post-doctoral fellow. At Carnegie Mellon he did much of his seminal work on multiple-scattering band-structure work, now known as the KKR method. His association with Bell Labs got him involved with semiconductor physics, and produced a long and fruitful collaboration with Luttinger (including, for example, development of the Luttinger-Kohn model of semiconductor band structure). In 1960 he moved to the newly founded University of California at San Diego, where he remained until 1979. He then accepted the Founding Director's position at the new Institute for Theoretical Physics in Santa Barbara. He took his present position as a professor at University of California at Santa Barbara in 1984; he is currently a Professor Emeritus.

Kohn very significant contributed to semiconductor physics, which lead to his award of the Oliver E. Buckley Prize by the American Physical Society for his work on solids. He was also awarded the Feenburg medal for his contributions the many-body problem. His work on density functional theory was initiated during a visit to the ENS in Paris, with Pierre Hohenberg, and was prompted by a consideration of alloy theory. The Hohenberg-Kohn theorem was further developed, in collaboration with Lu Sham, to produce the Kohn-Sham equation. The latter is the standard work horse of modern materials science, and even used in quantum theories of plasmas. In 2004, a study of all citations to the Physical Review  journals from 1893 until 2003, found Kohn to be an author of five of the 100 papers with the "highest citation impact", including the first two.

Scientist with a great following

Walter Kohn is a well known and much loved figure in many European campuses. He was a regular visitor to Jacques Friedel's laboratory and Carl Moser's Laboratory (CECAM) in Orsay, Universite Paris IX. Another favorite stop for Kohn was in Switzerland, at the ETH. He has also visited the National Research Council of Canada, his Canadian Alma Mater the University of Toronto, Montreal and Sherbrooke whenever his itineraries permitted him to do so. He is equally at home in Denmark, Israel, England or France. He has students in virtually every part of the world.

In 1957, he relinquished his Canadian citizenship and became a naturalized citizen of the United States.

He is a member of the International Academy of Quantum Molecular Science.

References

Some publications

  • W. Kohn, An essay on condensed matter physics in the twentieth century, Reviews of Modern Physics, Vol. 71, No. 2, pp. S59-S77, Centenary 1999. APS
  • W. Kohn, Nobel Lecture: Electronic structure of matter — wave functions and density functionals, Reviews of Modern Physics, Vol. 71, No. 5, pp. 1253-1266 (1999). APS
  • D. Jérome, T.M. Rice, and W. Kohn, Excitonic Insulator, Physical Review, Vol. 158, No. 2, pp. 462-475 (1967). APS
  • P. Hohenberg, and W. Kohn, Inhomogeneous Electron Gas, Physical Review, Vol. 136, No. 3B, pp. B864-B871 (1964). APS
  • W. Kohn, and L. J. Sham, Self-Consistent Equations Including Exchange and Correlation Effects, Physical Review, Vol. 140, No. 4A, pp. A1133-A1138 (1965). APS
  • W. Kohn, and J. M. Luttinger, New Mechanism for Superconductivity, Physical Review Letters, Vol. 15, No. 12, pp. 524-526 (1965). APS
  • W. Kohn, Theory of the Insulating State, Physical review, Vol. 133, No. 1A, pp. A171-A181 (1964). APS
  • W. Kohn, Cyclotron Resonance and de Haas-van Alphen Oscillations of an Interacting Electron Gas, Physical Review, Vol. 123, pp. 1242-1244 (1961). APS

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