Walter Kohn

Theoretical physicist Walter Kohn (born 1923) received the 1998 Nobel Prize in Chemistry for developing the density functional theory. The revolutionary theory, which became widely applied in the field of chemistry, physics, and materials science, substantially changed how scientists viewed the electronic structure of atoms, molecules, and solid materials. Kohn also made significant contributions to the physics of semiconductors, superconductivity, surface physics and catalysis.

The early life of the theoretical physicist was as dramatic as his later scientific contributions. Kohn personally experienced major events during the bloodiest period in modern history. His parents were victims of the Nazi Holocaust, and he observed the devastation that World War II wrought in his European homeland. He later moved to the United States at a time when the country unveiled a horrifying new weapon, the atomic bomb. As a result, he became an outspoken pacifist, and he would later seek to find less destructive applications for quantum physics, a field that he would help revolutionize.

He was born as Walter Samuel Gerst Kohn on March 9, 1923, in Vienna, Austria, to Salomon and Gittel Kohn. He was raised in a middle class Jewish family. Kohn described his mother as a highly educated woman, well versed in German, Latin, Polish and French and possessing some knowledge of Greek, Hebrew, and English. His father ran a printing business. According to Kohn, the main products of this business were high quality, artistic postcards, with designs most often based on paintings by contemporary artists commissioned by the firm. The business flourished in the early part of the twentieth century, but in the 1920s and 1930s it fell on hard times, primarily due to a worldwide economic depression.

Kohn's early education focused on Latin and Greek. His favorite subject was Latin and, ironically enough, he had little interest in mathematics. However, he did demonstrate an interest in physics at an early age. Still, his parents anticipated that he would take over the family business, a prospect that Kohn looked forward to with little enthusiasm. However, world affairs substantially changed the direction of his life.

Parents Died at Auschwitz

In 1938, when Kohn was 15 years old, Austria was annexed by Nazi Germany. As his family was Jewish, Kohn was expelled from public school by Austrian officials and was transferred to an all-Jewish school, where he studied for two years. His experience at the school would influence his educational direction, as he was inspired by one of his teachers, Emil Nohel, who had worked with famed scientist Albert Einstein. Nohel exposed Kohn to his analysis of Einstein's groundbreaking theories.

In 1939 Kohn's parent sent him and his sister to England, where Kohn lived with one of his father's business associates. In this way, the brother and sister were spared the horrors of the Holocaust. However, Kohn's parents weren't as fortunate. Salomon and Gittel Kohn were both later murdered at the German concentration camp at Auschwitz.

In England Kohn worked on a farm until he suffered a physically debilitating bout of meningitis. In 1940, during the German Blitzkreig, British authorities sent Kohn to an internment camp on the Isle of Man because he had a German passport. Only 17 years old, Kohn suffered harsh conditions and food shortages. He was then transferred to Quebec, Canada, where he spent the next year and a half in different camps. But the move proved fortunate: conditions were less harsh at the Canadian camps, and Kohn met a family whose sponsorship later enabled him to attend the University of Toronto.

Despite his incarceration, Kohn now considered himself a Canadian. He felt the country treated him well, and he harbored a strong bitterness toward Austria. When he was released from Canadian internment camps in 1943, he voluntarily enlisted in the Canadian Infantry Corps. That same year he enrolled at the University of Toronto. Even though he had never completed high school, Kohn earned bachelor's degrees in mathematics and physics.

Moved to America

In 1946 Kohn earned a master's degree in applied mathematics at the University of Toronto. He even published his first research paper, on applied mathematics, before completing his undergraduate work. His master's degree led to a fellowship at Harvard University in the United States. Originally, following the completion of the fellowship, Kohn had planned to return to Canada. However, he could not find a position in that country, so he remained in the United States, where he studied nuclear physics at Harvard with future Nobel laureate Julian Schwinger. He earned his doctorate in only two years. Except for two years he later spent at the Niels Bohr Institute in Copenhagen, Denmark, Kohn would remain in the United States.

After acquiring his physics Ph.D in 1948, Kohn served as an instructor at Harvard for two years. In 1950 he became a professor at Carnegie-Mellon University in Pittsburgh, Pennsylvania, where he taught for 10 years. On June 19, 1955, he married Mara Schiff. The couple would have three children: Sharon Ruth, Martin Steven, and Thomas David. In 1957, Kohn became a naturalized citizen of the United States.

At Carnegie-Mellon, in addition to teaching, Kohn sought to find ways of applying the quantum theory to semiconductors, a new technology at the time. In 1960 he moved to San Diego, California, where he served as a professor at the University of California and sought even broader applications of the theory. His work in this area would later culminate in a Nobel Prize in chemistry in 1998.

Developed Density-Functional Theory

After the first major paper on quantum mechanics was published in 1926, it became possible, on a theoretical level, to comprehend how subatomic particles interacted to form molecules. Before the structure of a molecule and its interactions could be known, scientists needed to know the geometrical arrangements of its atoms and how its components united to exchange energy. They believed they were able to determine how each electron of each atom would perform during interactions, but practical applications of these laws resulted in equations that were, as indicated by Paul Dirac, the co-founder of quantum physics, "too complex to be solved."

Kohn's research would help simplify the issues, as he would show that it wasn't necessary to track the motions of each individual electron. In 1964 Kohn, collaborating with colleague Pierre Hohenberg, demonstrated what would come to be known as the "density-functional theory," which suggested that it is only necessary to know the average number of electrons located at any given point in space (electron density) to make the appropriate calculations that determine a molecule's properties. Kohn and Hohenberg proved the existence of a universal, constant relationship (called the "density functional") between the structure of a molecular system and the arrangement of its electrons. Physicists sought ways to define this "density functional." Kohn himself, working with L. J. Sham in 1965, came up with a set of equations that served as an approximation. Still, these equations required refinement over the course of three decades before they could be of any practical use to chemists. British scientist John A. Pople from Northwestern University in Evanston, Illinois, would provide the most important breakthrough.

Received Nobel Prize in Chemistry

In 1970 Pople, later the co-recipient of the 1998 Nobel Prize in chemistry with Kohn, designed the GAUSSIAN computer program to model and test structures of small molecules. In 1992 he integrated the "density functional" into his program. This made the program faster and more accurate in analyzing larger molecules and complex interactions. In turn, it made the principles of quantum physics applicable to chemistry.

The combined work of Kohn and Pople had a dramatic impact on various fields of research. It made it possible to construct, according to the laws of quantum chemistry, computer models of molecules that could not be replicated in a laboratory setting.

In 1998 the Royal Swedish Academy of Sciences awarded the Nobel Prize in Chemistry to both Kohn and Pople, lauding the two scientists' pioneering contributions in developing methods that could be used for theoretical studies of the properties of molecules and the chemical processes in which they are involved.

Headed New Institute

Kohn stayed at the University of California at San Diego until 1979, when he became the first director of the National Science Foundation's new Institute of Theoretical Physics, located at the University of California in Santa Barbara. Kohn's leadership helped the Institute become one of the world's foremost research facilities, as it brought together international scientists to work on the most complex issues in theoretical physics and related areas. The Institute, under Kohn's leadership, was instrumental in developing new applications for quantum theory. He served as director from 1979 to 1984, and he served as a professor at the university from 1984 to 1991, when he was named professor emeritus and research professor.

Retired in California

Since retiring from teaching in 1991, Kohn has dedicated himself full time to research. He lives in Santa Barbara with his wife, Mara. In his spare time he pursues hobbies and interests that include classical music, reading (especially French literature), and cooking. He remains physically active by taking walks alone or with his wife and by roller blading once a week. He also enjoys spending time with his family, as all three of his daughters and his three grandchildren live in California.

In addition to receiving the Nobel Prize, Kohn was awarded the National Medal of Science in 1988. He was named to the American Academy of Arts and Sciences in 1963 and the National Academy of Sciences in 1969. He is also a member of the American Association for the United Nations. He served as president in 1962–63 and has been a member of its board of directors since 1963. He is a member of numerous other professional, scientific, and social organizations, and has authored numerous books and more than 200 articles and reviews that have been published in scientific journals and popular periodicals.

During his teaching career he was a visiting scholar at many universities in the United States and in Europe, including the University of Pennsylvania, the University of Michigan, the University of Paris, the University of Jerusalem, and Imperial College in London. He also served on many advisory boards and committees.

Promoter of Humanitarian Causes

Though he was born in Austria and became an American citizen, Kohn considers himself a citizen of the world. His scientific work coupled with his life experiences helped break down, in his own mind, the barriers of national borders and geographic boundaries. Still, he has a great affection for Canada, Denmark, England, France and Israel, as he lived and worked in these countries throughout his life. However, because of his early life experiences and the death of his parents, he still has some bitterness toward Austria, his homeland. And perhaps because of his harsh memories, Kohn has retained a strong sense of Jewish identity. Throughout his life he has remained committed to applying quantum mechanics toward peaceful purposes and has also worked to promote pacifist and environmentalist causes. He served on the advisory board of the Statewide Institute of Global Conflict and Cooperation from 1982 to 1992, and actively lobbied to stop nuclear physics projects at places such as Los Alamos. In 1992 Kohn joined 1,700 other leading scientists in signing the "Warning to Humanity," a statement that sounded an alarm about international environmental issues such as global warming.

Periodicals

Daily Nexus, January 17, 2001.

Online

"Walter Kohn," Biography Resource Center Online, http://www.galenet.galegroup.com/servlet/BioRC (December 8, 2006).

"Walter Kohn: Nobel Prize in Chemistry in 1998," Indian Academy of Sciences, http://www.ias.ac.in/currsci/jun10/articles18.htm (December 8, 2006).

"Walter Kohn: Nobel Prize in Chemistry, 1998," NobelPrize.org, http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1998/kohn-autobio.html (December 8, 2006).

"Walter Kohn," Notable Scientists: From 1900 to the Present, http://www.galenet.galegroup.com/servlet/BioRC (December 8, 2006).

"Walter Kohn," Walter Kohn Website, http://www.physics.ucsb.edu/∼kohn/ (December 8, 2006).

"Walter S(amuel) G(erst) Kohn," Contemporay Authors Online, http://www.galenet.galegroup.com/servlet/BioRC (December 8, 2006).