RETROSPECTIVE

Walter Kohn (1923–2016) RETROSPECTIVE

Douglas J. Scalapinoa,1 and Robert Sugara

Walter Kohn, who died on April 19, 2016, once said “Physics isn’t what I do; it is what I am.” Indeed, Walter was a world-renowned physicist, winner of the 1960 Oliver E. Buckley Prize for his prediction of anomalies in the phonon spectrum in metals, the 1977 Davisson– Germer Prize with Nortan Lang for their studies of the inhomogeneous interacting electron gas at surfaces, and the 1991 Eugene Feenberg Medal for the develop- ment of density-functional theory. However, it was in Chemistry that Walter received the ultimate scientific recognition. The 1998 Nobel Prize in Chemistry was shared by Walter Kohn, “for his development of the density-functional theory,” and John A. Pople, “for his development of computational methods in quantum chemistry.” The Nobel Committee recognized Walter’s work in the 1960s with postdoctorates Pierre Hohenberg (Bell Labs) and Lu Sham (University of California, San Diego) in the development of the density-functional theory in which the properties of a many-electron sys- tem can be determined by using functionals of the spatially dependent electron density. This theory is Walter Kohn. Image courtesy of the Office of Public Affairs and Communications, University of California, Santa Barbara. among the most widely used methods for determining the electronic structure and properties of complex molecules and solids. Insight into this work, as well coming into a situation in which the outside commu- as the remarkable story of Walter’s introduction to nity had mixed feelings about the establishment of physics at a segregated high school for Jews in Vienna such an institute. Fortunately, Walter accepted this and his subsequent escape from the Nazis by the challenge and in April 1978 the NSF Science Board Kindertransport, are recounted in an excellent article approved funding for an initial period of five years, by Andrew Zangwill (1). Here, in this brief retrospective, noting carefully that there was no certainty of continued we recount another aspect of Walter’s remarkable ca- support. So, in the fall of 1979 when Walter and his wife reer: his time at the University of California, Santa Barbara Mara arrived in Santa Barbara, the institute faced both (UCSB), beginning in 1979 when he became the first doubts from the community and uncertainty of long- Director of the National Science Foundation’s (NSF) term NSF support. However, Walter’s ability to relate Institute for Theoretical Physics (ITP). to the outside physics community and his judgment In 1978 the UCSB proposal for an institute for regarding both physics and people soon began to theoretical physics was to go before the NSF Science change things. He persuaded leading members of Board. To obtain the approval of the Board it was the physics community to serve on the ITP Advisory essential that the institute have a distinguished director Board and to put tremendous effort into the develop- from outside of Santa Barbara. Walter was an ideal ment of ITP’s scientific programs. Under Walter’s lead- choice, given his scientific breadth and leadership ership, a wide range of programs, proposed by the ability. However, although the institute, now called community and by members of the Advisory Board, the Kavli Institute for Theoretical Physics, is in its 37th were scheduled and successfully run. In addition, there year and internationally recognized, this was not were appointments of leading physicists as permanent initially the case. Walter, if he accepted, would be members, including Frank Wilczek, J. Robert Schrieffer,

aDepartment of Physics, University of California, Santa Barbara, CA 93106 Author contributions: D.J.S. and R.S. wrote the paper. The authors declare no conflict of interest. 1To whom correspondence should be addressed. Email: [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1609988113 PNAS | August 9, 2016 | vol. 113 | no. 32 | 8883–8884 Downloaded by guest on September 26, 2021 and James Langer. Finally, Walter’s creation of a wel- in the campus community. Particularly memorable coming atmosphere made the institute a place where was their support of a concert in which Ullmann’s physicists, ranging from new doctorates to senior Quartet No. 3—composed while Ullmann was a prisoner leaders of the field, wanted to visit. Walter set the di- at Theresienstadt concentration camp in 1943 and gassed rection and established the atmosphere that led to the at Auschwitz-Birkenau on October 18, 1944—was played. Kavli Institute for Theoretical Physics becoming the Walter explained his support of this concert, saying: major center it is today. “My parents, Salomon and Gittel Kohn, were in the After stepping down as Institute Director, Walter Terezin (Theresienstadt) concentration camp with Viktor returned to teaching and research, mentoring additional Ullmann. I would like to think that they heard some of doctorate students at UCSB. With Alan Heeger he his beautiful music.” directed and produced a film The Power of the Sun, Although over 37 years have passed since Walter telling the story of photovoltaics, the first solar panels, became the first ITP director, his love of physics and his and where this technology could take us in the future. way of interacting with others lives on in Kohn Hall, which Walter worked with the Institut de la Vision in France houses the Kavli Institute for Theoretical Physics, in the to develop an optical corrective lens to treat macular UCSB Physics department and the UCSB campus, to degeneration. Walter and his wife Mara were active which he contributed so much.

1 Zangwill A (2014) The education of Walter Kohn and the creation of density-functional theory. Arch Hist Exact Sci 68(6):775–848.

8884 | www.pnas.org/cgi/doi/10.1073/pnas.1609988113 Scalapino and Sugar Downloaded by guest on September 26, 2021