[1] In 1966 he reformulated the coupled cluster method (originally developed in the 1950s for nuclear physics) for the study of electron correlation in atoms and molecules (and later worked together with colleague Josef Paldus).
He then enrolled at Charles University of Prague in the Faculty of Mathematics and Physics, during which time his father passed away in 1957, before he finished his Masters (RNDr) thesis in 1961 and received the Heyrovsky Medal [de] a year later for the contributions to polarography in his first 5 papers.
It was during this time that he proposed the use of the coupled cluster method for studying electron correlation in atoms and molecules, in his CSc doctoral dissertation, which was completed in 1964 (in the same year his son and first child was born) and defended in 1965.
[4] The 1968 Warsaw Pact invasion of Czechoslovakia interrupted Čížek's doctoral studies, which he was pursuing while working as a Junior Scientist at the Institute of Physical Chemistry in Prague, and forced him to leave his native country.
[4] The numerous research contributions of Čížek throughout his career, together with a complete bibliography of his 180 peer-reviewed publications, were summarized in the AIP Proceedings of the International Conference of Computational Methods in Science and Engineering in 2010.