Walter Kohn: From Refugee Child to Architect of Density Functional Theory

Walter Kohn (1923–2016) was an Austrian-born American-Canadian theoretical physicist who changed computational chemistry. With Pierre Hohenberg and Lu Jeu Sham, he created density functional theory, which allows scientists to calculate the properties of molecules and solids from their electron density. He shared the 1998 Nobel Prize in Chemistry with John Pople, although he was a physicist by training. His life story, from escaping Nazi-occupied Europe as a teenager to winning the Nobel Prize, is one of determination and quiet courage.

Early Life and Family

Walter Kohn was born on 9 March 1923 in Vienna, Austria, to a Jewish family. His father, Salomon Kohn, ran an art postcard publishing business, and his mother was Gittel Kohn. Walter grew up in a cultured, middle-class home. After Germany annexed Austria in 1938, his life changed completely. He was expelled from his school, and his parents were later murdered in the Holocaust. Kohn escaped to England on a Kindertransport, the programme which rescued Jewish children, in 1939. He has spoken about the loss of his parents as a painful part of his life. He took up studies in England and then in Canada.

Education and Mentors

In England, Kohn was sent to a school for refugees, and later he was interned as an "enemy alien" in 1940 and sent to Canada, where he was held in camps in Quebec and New Brunswick. After his release, he studied at the University of Toronto, earning a bachelor's degree in mathematics and physics in 1945 and a master's degree in applied mathematics in 1946. He served for a short time in the Canadian Army. He then went to Harvard University, where he obtained his PhD in physics in 1948 under Julian Schwinger, who later won the Nobel Prize in Physics (1965). Kohn learned the style of rigorous theoretical physics from Schwinger.

Career Timeline

Major Scientific Contributions

• Solid-state physics. Early in his career he worked on the electronic structure of solids, including the Kohn–Luttinger work on superconductivity and the Korringa–Kohn–Rostoker (KKR) method for band structure.
• Kohn anomaly and Friedel-type effects. He studied how metals respond to lattice vibrations, leading to the "Kohn anomaly" in phonon dispersion.
• Density functional theory. The Hohenberg–Kohn theorems (1964) and the Kohn–Sham equations (1965) are his most famous contribution. See our discovery post for the equation E = E[ρ] and for the self-consistent cycle.
• Later work. He contributed to the theory of the electronic structure of atoms and molecules, to the development of better approximations and to the physics of nanostructures.

Awards, Honours and the Nobel Prize

The 1998 Nobel Prize in Chemistry was awarded half to Walter Kohn "for his development of the density-functional theory" and half to John A. Pople "for his development of computational methods in quantum chemistry". Kohn is one of the few physicists who have received the Nobel Prize in Chemistry. He also received the Oliver E. Buckley Prize for condensed matter physics, the Davisson–Germer Prize, and many other honours, and he was a member of the US National Academy of Sciences.

Personality, Struggles and Lesser-Known Facts

• Refugee scholar. Kohn and his sister were saved, but their parents died. This experience stayed with him all his life.
• Not a chemist. He was trained as a physicist, and the Chemistry Prize showed how far his method had spread. Chemists adopted it because it was practical.
• Simple ideas. Kohn was known for liking physical clarity and general principles, such as his work on the "nearsightedness" of electronic matter, which says that local properties depend mainly on nearby potentials.
• Founding director. He helped to set up the Institute for Theoretical Physics (now the Kavli Institute for Theoretical Physics) at UC Santa Barbara, a major international centre which hosts visiting scientists.
• Beyond physics. He was known as a thoughtful person who cared about the role of science in society.

Legacy and Influence on Modern Chemistry

DFT is now the most widely used method for electronic-structure calculations in chemistry, physics and materials science. Papers on DFT are among the most cited in all of science. It allows researchers to study catalysts, drugs, batteries and solar materials. Kohn's work also strengthened the link between physics and chemistry: concepts like electron density, Fermi level and band structure are now used by chemists as naturally as orbitals. Many M.Sc. courses in India include DFT, and research groups use it for materials for solar cells, hydrogen storage and catalysis.

Lessons for Students

1. Simplify the problem. Replacing a 3N-variable wavefunction with a 3-variable density made impossible problems doable.
2. Cross boundaries. A physicist transformed chemistry. Learn mathematics, physics and chemistry together.
3. Resilience matters. Kohn lost his family and homeland but built a career of lasting value.
4. Collaboration. Hohenberg and Sham were young co-authors on the two historic papers.

FAQ

Was Walter Kohn a chemist?

No. He was a theoretical physicist, but he received the Nobel Prize in Chemistry for a theory that is central to chemistry.

Who was his doctoral supervisor?

Julian Schwinger at Harvard University, a Nobel Prize winner in Physics.

What are the two main DFT papers?

The 1964 paper by Hohenberg and Kohn and the 1965 paper by Kohn and Sham.

Where did he spend most of his later career?

At the University of California, first in San Diego and then in Santa Barbara, where he worked until the end of his life.

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