Clemens C. J. Roothaan: FC = SC$_{epsilon}$

摘要

Clemens Carel Johannes Roothaan was born in Nijmegen, the Netherlands, on 29 August 1918. After completing his study at the gymnasium (high school), he enrolled to study electrical engineering at the Technical University of Delft in 1935. During his study at Delft, he was not satisfied with the course curriculum and was inclined towards subjects more focused on physics. To enrich his understanding of various topics in physics, he spent the spring of 1939 at the Technical University of Karlsruhe for auditing classes. He came back to Nijmegen in the summer of 1939. Soon after, World War II was declared, and he was inducted to the Royal Engineers Regiment of the Netherlands army, along with inmates, mostly graduates of the University of Delft. Despite other responsibilities, he could continue with his study there. Later, he along with his brothers were sent to the police lock-up in Hengelo, where he again managed to continue his studies with the resources available from the university library. After three and half months, he was sent to a Nazi concentration camp at Vught. At Vught, he was invited to join the company of the electronic giant N V Philip, who had set up a small manufacturing plant at the camp. Here, he got involved with the Kronig–Penny calculation of Schr ¨odinger equation for a one-dimensional crystal. After the successful completion of the project, he was given a more ambitious project to calculate elastic constants in a classical crystal. This project was formulated in consultation with his professors at Delft. He could again successfully complete the project, and this work was accepted for his Master’s thesis in Delft. Soon after the camp at Vught was evacuated, Roothaan was sent to another Nazi camp at Sachsenhausen. Life at Sachsenhausen was much more difficult than at Vught. Here, he was given the job of a draftsman and later an electrician, and he stayed in the camp until its final evacuation. After that, he was repatriated to the Netherlands, returned to Delft, and officially granted diploma Ingenieur (engineer) on 15 October 1945 [1].