Clemens C. J. Roothaan

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Clemens C.J. Roothaan was born in 1918 in Nijmegen, the Netherlands. He did his PhD thesis with Robert S. Mulliken from the University of Chicago, on semiempirical MO theory, while holding a post at the 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. 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 math 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.