Walter Kohn

Walter Kohn – Life, Thought, and Enduring Legacy in Physics & Chemistry

: Discover the remarkable journey of Walter Kohn (1923–2016), the Austrian-American theoretical physicist whose development of density functional theory transformed how scientists model electronic systems.

Introduction

Walter Kohn is a towering figure in twentieth-century science: though born in Austria, he became an integral part of American physics and chemistry. His crowning achievement—density functional theory (DFT)—reshaped how researchers compute and understand the electronic structure of atoms, molecules, and solids. Awarded the Nobel Prize in Chemistry in 1998 (shared with John Pople), Kohn’s work bridged physics, chemistry, materials science, and computational methods. Yet his life also carried a powerful human narrative: fleeing persecution, enduring internment, and rebuilding a scientific career from scratch.

Early Life, Exile & Education

Childhood in Vienna & Jewish Identity

Walter Kohn was born on March 9, 1923 in Vienna, Austria to a Jewish family. Anschluss (annexation of Austria) in 1938, his Jewish background made life dangerous.

In 1939, Kohn and his sister were sent to England via the Kindertransport, a rescue effort to evacuate Jewish children from Nazi territories.

Internment, Canada, and University Years

When World War II escalated, Britain and its allies interned a number of “enemy aliens” from Axis countries—even refugees. Kohn was among those detained, and in 1940 he was relocated to Canada, to a camp near Sherbrooke, Québec.

After release, Kohn enrolled at the University of Toronto, where he studied mathematics and physics. Because, as an interned “enemy alien,” he was barred from entering the chemistry building, he gravitated toward physics and mathematics.

Kohn then went to Harvard University, where he completed a Ph.D. in physics (1948), working under the supervision of Julian Schwinger.

Academic & Scientific Career

Early Appointments & Contributions

Following his doctoral training, Kohn held a postdoctoral appointment in Copenhagen, then joined Carnegie Mellon University (then Carnegie Institute of Technology) from about 1950 to 1960. solid state physics, multiple-scattering methods, and semiconductor theory, collaborating with other luminaries such as Joaquin Luttinger.

In the 1960s, Kohn joined the University of California, San Diego (UCSD), continuing his research in condensed matter theory.

In 1979, he moved to the University of California, Santa Barbara (UCSB), where he became founding director of the Institute for Theoretical Physics (which later became the Kavli Institute for Theoretical Physics).

At UCSB, the institute building was even named Kohn Hall in his honor, reflecting his foundational role in the institution’s theoretical physics mission.

Key Scientific Contributions & Impact

Density Functional Theory (DFT) & the Hohenberg–Kohn Theorems

Kohn’s hallmark contribution is the development of density functional theory (DFT). In contrast to the traditional many-electron wavefunction approach (which scales poorly as systems get large), DFT reformulates quantum mechanics by focusing on the electron density — a function of three spatial variables — rather than a multi-­dimensional wavefunction.

The Hohenberg–Kohn theorems establish that the ground-state density uniquely determines the external potential and thus all properties of the system, and that there exists a functional of the density that yields the ground-state energy.

Kohn, together with Lu Jeu Sham, further developed Kohn–Sham equations, which introduce an auxiliary non-interacting system to approximate the interacting system, making the computation of practical and accurate DFT calculations possible.

Because of these innovations, DFT has become the workhorse for computational materials science, quantum chemistry, condensed matter physics, and nanoscience.

Other Theoretical Roles & Methods

Beyond DFT, Kohn made significant contributions to:

• Multiple-scattering (KKR) methods for electronic band structure in solids

• Luttinger–Kohn model in semiconductor physics, relating to band structure in the presence of periodic potentials

• Work on surface physics, catalysis, superconductivity, and the theory of the insulating state

His contributions earned him many honors during his lifetime, including:

• Oliver E. Buckley Prize (1961) from the American Physical Society

• National Medal of Science (1988)

• Nobel Prize in Chemistry, 1998, shared with John Pople, “for his development of the density-functional theory.”

He was also elected to the National Academy of Sciences (1969) and was a foreign member of the Royal Society and other academies.

Character, Challenges & Personal Reflections

Kohn’s life was marked by resilience, curiosity, and humility. The trauma of exile and loss in his youth shaped his worldview. In his Nobel autobiographical reflections, he described the joy and privileges of doing science, the delight of collaboration with younger researchers, and his simple pleasures in life: reading French literature, walking with his wife Mara, browsing classical music, and cooking (notably claiming pride in his ratatouille)

His scientific personality combined deep theoretical insight with a pragmatic sense of what methods would be computationally useful. He valued precision, elegance, and clarity in argumentation — traits evident in how DFT matured from pure theory to practical algorithms.

He also remained engaged beyond his scientific niche: participating in community life in Santa Barbara, maintaining intellectual curiosity long past official retirement, and welcoming cross-disciplinary dialogue.

Famous Quotes & Insights

While Kohn was less of a public quote-maker than philosophers or political figures, the statements he left in his Nobel lectures, interviews, and writings convey deep intellectual modesty and vision. Some representative ideas include:

“The total electron density of a system is sufficient to determine all ground-state properties of that system.”
— Core principle underlying DFT (i.e. Hohenberg–Kohn theorem)

“I still love doing physics … mostly together with young people less than half my age.”

He emphasized the shift from wavefunctions to densities as not merely computational convenience but conceptual: that one might encode rich many-body physics into simpler variables. (Implied in his formulations in Nobel lecture)

These statements reflect his combined focus on elegance, utility, and the human dimension of scientific life.

Legacy & Lessons

Transformative Scientific Legacy

• Kohn’s DFT fundamentally reshaped how electronic structure is computed — nearly all modern materials, chemical, and molecular modeling makes use of variants of his ideas.

• His approach bridged theory and computation, showing how foundational physics could directly empower applied research in chemistry, materials, and nanotechnology.

• Many scientists consider DFT as one of the greatest intellectual tools developed in the latter half of the 20th century in physical science.

Human & Ethical Lessons

• His journey from refugee and interned youth to Nobel laureate embodies resilience, persistence under oppression, and the possibility of rebuilding.

• Kohn’s humility, openness to collaboration, and lifelong curiosity offer a model for scientists who combine deep specialization with human values.

• He demonstrated that theoretical work, when properly framed, can lead to vast practical impact — reminding us that abstraction and application are not necessarily opposed.

Institutional Influence

• At UCSB, his role in founding the Institute for Theoretical Physics (Kavli Institute) helped catalyze a major center for theoretical research.

• He mentored and collaborated with many younger physicists and chemists, helping propagate his ideas into new domains.

Conclusion

Walter Kohn’s life is a rich tapestry of intellectual daring, personal struggle, and lasting contribution. From a child refugee fleeing Nazism, he rose to reshape scientific computation and theory in ways few ever have. His work reminds us that deep conceptual insight, allied with a sense of mathematical elegance and computational pragmatism, can transform entire fields.