Clemens C. J. Roothaan

Clemens C.J. Roothaan (born in 1918 in Nijmegen) is a Dutch physicist.

He enrolled TU Delft in 1935 to study electrical engineering. During World War II he was first detained as a prisoner of war camp, later he was sent for a year to a concentration camp in Vught. 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. The work he was assigned to while cooperating with Philips was a foundation for his master's thesis. He obtained his masters degree in physics from TU Delft on October 14, 1945. After that he moved to USA, where he did his PhD thesis with Robert S. Mulliken from the University of Chicago, on semiempirical MO theory, while holding a post at The Catholic University of America in Washington, D.C.. He realised that the then current approach to molecular orbital theory was incorrect and changed his topic to what resulted in the development of the Roothaan equations. Prof. Mulliken mentions this work in his Nobel lecture as follows:

I tried to induce Roothaan to do his Ph.D.thesis on Hückel-type calculations on substituted benzenes. But after carrying out some very good calculations on these he revolted against the Hückel method, threw his excellent calculations out the window, and for his thesis developed entirely independently his now wellknown all-electron LCAO SCF self-consistent-field method for the calculation of atomic and molecular wave functions, now appropriately referred to, I believe, as the Hartree-Fock-Roothaan method.

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 Centre. 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 Laboratories in Palo Alto, California, where his primary contribution has been in the development of the mathematical coprocessor routines for the Itanium chip. His method of analyzing pipeline architecture has been unique and innovative and greatly admired in supercomputer circles around the world.

He is a member of the International Academy of Quantum Molecular Science.

References

• C.C.J. Roothaan : My Life as a Physicist : Memories and Perspectives. J. Molec. Struct. (Theochem) 234,1-12 (1991).

External links

• A brief description of his life and work, part autobiographical from the above reference.