Prof. Emeritus Clemens C.J. Roothaan turns 100 on August 29th

August 23, 2018

A young Clemens C.J. Roothaan, wearing glasses and a suit. stands.

University of Chicago Photographic Archive, apf7-01109, Special Collections Research Center, University of Chicago Library.

I haven’t written a note like this before, but I do think it’s time to congratulate one of our fellowship who is about to achieve his one hundredth birthday. Louis Block Professor Emeritus Clemens C. J. Roothaan will turn 100 on August 29th. I am indebted to Robin Mitchell for the following account of Professor Roothaan’s fascinating life:


"Clemens Roothaan was born in Nijmegen, Holland, in 1918, into an upper-class family. When the Nazis invaded Holland, Clemens and his two younger brothers were in university, all of which were closed down owing to the invasion. Clemens’ younger brother, Vic, was in the resistance and evaded capture, but the Nazis took Clemens and their youngest brother, John, instead. The two of them were first housed in the local jail and eventually moved to Vught concentration camp. While there, Clemens was forced into slave labor at Phillips Electric, but was also able to continue his studies.

Near the end of the war, the brothers were moved to Sachsenhausen concentration camp. Shortly after that they were separated and Clemens started on a death march to the Baltic Sea while John went to Bergan-Belsen, where he succumbed to typhus. The initial plan for the death march was to put those who survived the march onto ships, and then torpedo the ships. However, when Hitler killed himself, the guards began to desert their posts, leaving the prisoners on their own. The brothers continued on, heading west. On May 2nd, 1945, they met American troops, halfway between Berlin and Denmark. Clemens was repatriated to Holland by the end of the month.

In September, he returned to Delft to finish his studies. He received the equivalent of a Masters Degree. He then accepted a post-graduate fellowship at the University of Chicago, where he studied nuclear physics and quantum mechanics, starting in 1946. Working under future Nobel laureate, Robert Mulliken, Clemens began his PhD work on semi-empirical MO calculation on substituted benzenes. He was passionate about quantum chemistry before that field had a name. As he began working out the calculations he realized that all MO calculations started with a "one-electron Hamiltonian theory.” (In quantum mechanics, a Hamiltonian is an operator corresponding to the total energy of a system in most of the cases). Clemens, not being satisfied with the idea of a one-electron Hamiltonian theory, began thinking intensely about it and, while listening to the Chicago Symphony under the stars, had the epiphany that standard MO theory had started with the wrong question. This realization led him to the development of "the Roothaan equations."

While he was doing his PhD work, he taught at Catholic University of America in Washington D.C., traveling back and forth to Chicago to consult with Mulliken. Clemens returned to Chicago to teach physics and chemistry, eventually starting the department of computer science at the University of Chicago in 1949. He remained on active duty until retiring in 1988. Having done consulting work in computer sciences, he soon went to work for Hewlett Packard, where, over a period of fifteen years, he developed the mathematical co-processor routines for the Itanium chip. After his retirement from Hewlett Packard, he continued to do consulting work. He traveled all over the world with his late wife, Judith.

Clemens continues to live in the Hyde Park home where he and Judy raised their five children. Until just a few years ago he was still working on computer equations."


With my greetings and warmest congratulations to Professor Roothaan.

-David Bevington, Prof. Emeritus and Co-Chair of the Emeriti Faculty Steering Committee