Clemens C. J. Roothaan (August 29, 1918 – June 17, 2019) was a Dutch physicist and chemist known for his development of the self-consistent field theory of molecular structure.

Biography

Roothaan was born in

Nijmegen Nijmegen ( , ; Nijmeegs: ) is the largest city in the Dutch province of Gelderland and the ninth largest of the Netherlands as a whole. Located on the Waal River close to the German border, Nijmegen is one of the oldest cities in the ...

. He enrolled

TU Delft The Delft University of Technology (TU Delft; ) is the oldest and largest Dutch public university, public Institute of technology, technical university, located in Delft, Netherlands. It specializes in engineering, technology, computing, design, a ...

in 1935 to study

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

. Roothaan was studying physics at university when World War II broke out. As a Catholic citizen, he was temporarily allowed to continue studying. During World War II his brother Vic was involved with the Dutch Resistance, and when German soldiers came to the house looking for him they didn’t find Vic, but took Clemens Roothaan and his younger brother Jan instead. Later he and his brother Jan were sent to the

Vught Vught () is a municipality and a town in the Province of North Brabant in the southern Netherlands, and lies just south of the industrial and administrative centre of 's-Hertogenbosch. Many commuters live there, and in 2004 the town was named "Best ...

concentration camp A concentration camp is a prison or other facility used for the internment of political prisoners or politically targeted demographics, such as members of national or ethnic minority groups, on the grounds of national security, or for exploitati ...

for suspected involvement with the Dutch Resistance. On September 5, 1944, the remaining prisoners of the camp (including the Roothaan brothers) were moved to the Sachsenhausen camp in Germany ahead of the advancing Allies. Near the end of the war, the Sachsenhausen inmates were sent on a

death march A death march is a forced march of prisoners of war, other captives, or deportees in which individuals are left to die along the way. It is distinct from simple prisoner transport via foot march. Article 19 of the Geneva Convention requires tha ...

which Roothaan's brother did not survive. While a prisoner of war he was able to pursue his studies in physics together with other professors and students under the formal guidance of

Philips Koninklijke Philips N.V. (), simply branded Philips, is a Dutch multinational health technology company that was founded in Eindhoven in 1891. Since 1997, its world headquarters have been situated in Amsterdam, though the Benelux headquarter ...

. The work he was assigned to while cooperating with Philips was a foundation for his master's thesis. He obtained his master's degree in physics from

on October 14, 1945. After that he moved to USA, where he did his PhD thesis with

Robert S. Mulliken Robert Sanderson Mulliken Note Longuet-Higgins' amusing title "Selected ploddings of Robert S Mulliken" for reference B238 1965 on page 354 of this Biographical Memoir. The title should be "Selected papers of Robert S Mulliken." (June 7, 1896 � ...

from the

University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...

, on semiempirical MO theory, while holding a post at

The Catholic University of America The Catholic University of America (CUA) is a private Catholic research university in Washington, D.C., United States. It is one of two pontifical universities of the Catholic Church in the United States – the only one that is not primarily ...

in Washington, D.C.. He realised that the then current approach to

molecular orbital theory In chemistry, molecular orbital theory (MO theory or MOT) is a method for describing the electronic structure of molecules using quantum mechanics. It was proposed early in the 20th century. The MOT explains the paramagnetic nature of O2, whic ...

was incorrect and changed his topic to what resulted in the development of the

Roothaan equations The Roothaan equations are a representation of the Hartree–Fock equation in a non orthonormal basis set which can be of Gaussian-type or Slater-type. It applies to closed-shell molecules or atoms where all molecular orbitals or atomic orbitals ...

. Prof. Mulliken mentions this work in his Nobel lecture as follows: He had moved to the University of Chicago in 1949 and his PhD was awarded in 1950. He then joined the Physics Department of the University of Chicago. From 1962 to 1968 he was Director of the University of Chicago Computation Center. Later he was Professor of Physics and Chemistry at the University of Chicago. Since his retirement, in 1988, he has worked for the

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company. It was founded by Bill Hewlett and David Packard in 1939 in a one-car garage in Palo Alto, California ...

Laboratories in

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

, where his primary contribution has been in the development of the mathematical coprocessor routines for the

Itanium Itanium (; ) is a discontinued family of 64-bit computing, 64-bit Intel microprocessors that implement the Intel Itanium architecture (formerly called IA-64). The Itanium architecture originated at Hewlett-Packard (HP), and was later jointly dev ...

chip. His method of analyzing pipeline architecture has been unique and innovative and greatly admired in supercomputer circles around the world. In 1982 Roothaan became a correspondent of the

Royal Netherlands Academy of Arts and Sciences The Royal Netherlands Academy of Arts and Sciences (, KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed in the Trippenhuis in Amsterdam. In addition to various advisory a ...

. He was a member of the

International Academy of Quantum Molecular Science The International Academy of Quantum Molecular Science (IAQMS) is an international scientific learned society covering all applications of quantum theory to chemistry and chemical physics. It was created in Menton in 1967. The founding members we ...

and the Society of Catholic Scientists. He

turned 100 A centenarian is a person who has reached the age of 100. Because life expectancies at birth worldwide are well below 100, the term is invariably associated with longevity. The United Nations estimated that there were 316,600 living centenarian ...

in August 2018 and died in June 2019.

Works

Autobiographies

* *

References

External links

* {{DEFAULTSORT:Roothaan, Clemens 1918 births 2019 deaths Dutch men centenarians 20th-century Dutch physicists Dutch emigrants to the United States Dutch Roman Catholics Catholic University of America faculty Members of the International Academy of Quantum Molecular Science University of Chicago alumni University of Chicago faculty Delft University of Technology alumni People from Nijmegen Theoretical chemists Members of the Royal Netherlands Academy of Arts and Sciences Computational chemists

Biography

Works

Autobiographies

See also

References

External links