Walter Kohn - Chemists, Timeline and Facts

Walter Kohn was born on March 9, 1923 in Vienna, Austria, to Salomon and Gittel Kohn. His earliest memory of his childhood was that of being subjugated by the Austrian Nazi regime.

Kohn gained his early education from a public elementary school. He later enrolled at the Akademische Gymnasium where he developed an interest for Latin and Greek.

In 1938, when Hitler’s Germany annexed Austria, the Kohns’ were tarnished financially and socially. Their family business was confiscated and they were ripped off their freedom. Young Kohn was expelled from his school. Subsequently, he entered a Jewish school where he developed his interest in mathematics and science.

During World War II, Kohn was transported to England in the famous Kindertransport rescue operation, his parents being unable to leave Austria. He was first taken to England where he stayed with the Hauffs’ who had business relation with senior Kohn. However, since he had a German nationality, he was sent to Canada by the British. In Canada, Dr Bruno Mendel served as his guardian.

He finally settled at the camp in Trois-Rivieres, meant for German internees and refugees, in Canada. Kohn’s completed his high school studies from the educational facilities at the camp. Academically bright, he passed the McGill University junior Matriculation exam and exams in mathematics, physics and chemistry on the senior matriculation level.

Kohn successfully gained admission at the University of Toronto. Since he wasn’t allowed to enter the chemistry building, he opted for physics and mathematics instead. In 1945, he graduated with a BA in applied mathematics and a year later was awarded an MA in the subject.

Obtaining a Lehmann fellowship, Kohn entered the prestigious Harvard University. Under the guidance to Julian Schwinger, he worked on Green’s function variational method of three-body scattering problem as the subject for his thesis. In 1948, Kohn struck success by discovering an elementary formulation for variational principle of scattering. Same year, he was awarded a PhD degree in physics.

After completing his doctoral studies, Kohn remained in Harvard, serving as a researcher and teacher. For two years, he shared an office with Sidney Borowitz and assisted Schwinger in his work on quantum electrodynamics and the emerging field theory of strong interactions between nucleons and mesons.

While at Harvard, he also fell under the influence of Van Vleck and the sub-genre, solid state physics. Kohn even temporarily chaired Vleck’s position as a solid state physics teacher during the latter’s absence. The job gave him the opportunity to broaden his knowledge in a new arena of physics which was relatively lesser known to him.

In 1950, he secured a fellowship at the National Research Council in Copenhagen. Simultaneously, he also got a job at the Carnegie Institute of Technology. Requesting a leave of absence, he fulfilled his fellowship in Copenhagen. In Copenhagen, he turned to solid state physics. He served as a substitute teacher of the subject and did research on the subject along with Res Jost.

In 1952, he moved to Carnegie Institute of Technology. At Carnegie, he did much of his seminal work on multiple-scattering band-structure work, now known as the KKR method. Other work done by him include the image of the metallic Fermi Surface in the phonon spectrum, exponential localization of Wannier functions and the nature of the insulating state.

In 1953, supported by Van Vleck, he attained a summer job at Bell Labs as an assistant to W. Shockley. His project was on radiation damage of Si and Ge by energetic electrons, critical for the use of the then recently-developed semiconductor devices for applications in outer space. The Bell Labs, which the premier center for research in the field of solid state physics, became the summer home of Kohn where he returned every year until 1966.

Kohn’s association with Bell Labs got him involved with semiconductor physics. His collaboration with Luttinger bore fruitful results as the two came up with several unknown concepts in semiconductor physics including development of an effective Hamiltonian in the presence of magnetic fields, development of the first non-heuristic derivation of the Boltzman transport equation for quantum mechanical particles and development of the Luttinger-Kohn model of semiconductor band structure.

In 1960, Kohn took up an academic position as the Physics Department chair at the then newly founded University of California, San Diego. He spent a sabbatical semester at the Ecole Normale Superieure in Paris in 1963 when he initiated his work in the development of density functional theory.

Kohn’s quest to know whether an alloy is completely or only partially characterized by its electronic density distribution led to his unearthing of the act that for a single particle, there is an explicit elementary relation between the potential and the density of the ground-state. He realized that two different potentials with associated different groundstates could give rise to the same density distribution.

He laid the foundation for a theory that stated it was not necessary to account for every electron's movement. Instead, one could look at the average density of electrons in the space. His finding presented new opportunities for calculations involving chemical structures and reactions.

Along with his associate Pierre Hohenberg, Kohn came up with the Hohenberg Kohn (HK) variational principle that gave the details of his findings. The duo published the report with various approximations. The Hohenberg-Kohn theorem was further developed in association with Lu Jeu Sham. Kohn and Sham came up with the Kohn-Sham equations, which has become the standard work horse of modern materials science and is even used in quantum theories of plasmas

Kohn’s stint at the University of California, San Diego lasted until 1979. Following this, he accepted the Founding Director's position at the new National Science Foundation’s Institute for Theoretical Physics in Santa Barbara. Therein, he continued to work with post-doctoral fellows on DFT.

In 1984, Kohn took up the position of a professor in the Physics Department at the University of California at Santa Barbara. He continued to work there until the end of his life.

Kohn’s most significant contribution came with his development of the density-functional theory. All through his career, he used quantum mechanics to comprehend the electro bonding between atoms to form molecules. In 1964, he laid the foundation for a theory that stated it was not necessary to account for every electron's movement. Instead, one could look at the average density of electrons in the space. This gave the scientific world a better understanding and new insight for calculations involving chemical structures and reactions. It also simplified the computation needed to understand the electron bonding between atoms within molecules.

For his contribution in the field of semiconductor physics, he was awarded the Oliver E. Buckley Prize and the Davison Germer Prize by the American Physical Society. He also received the Feenburg Medal.

In 1988, he received the National Medal of Science.

In 1998, Kohn was bestowed with the prestigious Nobel Prize in Chemistry for his development of the density-functional theory. He shared the prize with John Pople.

Austria honoured him with the Austria Decoration for Science and Art award and Grand Decoration of Honor in Silver with Star for Services to the Republic of Austria.

He received an honorary doctorate degree from the University of Oxford and Harvard University.

He was elected as the Foreign Member of the Royal Society. Furthermore, he became a member of the American Academy of Arts and Sciences, National Academy of Sciences and the International Academy of Quantum Molecular Science. He became an honorary member of the Austrian Academy of Sciences.

Kohn was twice married in his lifetime. His first marriage was to Lois Adams and later on he married Mara Schiff.

He died of jaw cancer on April 19, 2016, at the age of 93.