I feel very honored that I have been asked to write a Foreword to this book. The subject of the book – “Coupled cluster theory” – has been around for about half a century. The basic theory and explicit equations for closed-shell ground states were formulated before 1970. At the beginning of the seventies the rst ab initio calcu- tion were carried out. At that time speed and memory of computers were very limited compared to today’s standards. Moreover, the size of one-electron bases employed was small, so that it was only possible to achieve an orientation in methodical aspects rather than to generate new signi cant results. Extensive use of the coupled-cluster method started at the beginning of the eighties. With the help of more powerful computers the results of coupled-cluster approaches started to yield more and more interesting results of relevance to the interpretation of experimental data. New ideas in methodology kept appearing and computer codes became more and more ef cient. This exciting situation continues to this very day. Remarkably enough, even the - quired equations can now be generated by a computer with the help of symbolic languages. The size of this monograph and the rich variety of articles it contains attests to the usefulness and viability of the couple-cluster formalism for the h- dling of many-electron correlation effects. This represents a vivid testimony of a tremendous work that has been accomplished in coupled-cluster methodology and its exploitation.

P. Cársky is a Senior Scientist at the Heyrovský Institute and external professor at the Charles University

J. Paldus is a Distinguished Professor Emeritus at the University of Waterloo, Canada

J. Pittner is the Head of the Department of Theoretical Chemistry at the Heyrovský Institute

P. Cársky was a coauthor of the following books:

R. Zahradník, P. Cársky: Organic Quantum Chemistry Problems. Plenum Press, New York 1973, 222 p.

New editions:

Hirokawa Publishing Company, Tokyo, 1979 (in Japanese), SNTL, Praha 1978 (in Czech).

R. Zahradník, P. Cársky: Sbírka úloh z aplikací kvantové chemie. Statní pedagogické nakladatelství, Praha 1967, 174 p (in Czech).

P. Hobza, P. Cársky, J. Pancír, R. Zahradník: Výklad k programum pro kvantove chemické výpocty. Státní pedagogické nakladatelství, Praha 1972, 140 p (in Czech).

P. Cársky, J. Pancír, R. Zahradník: Molekulové orbitaly v chemii. Academia, Praha 1974, 140 p (in Czech).

P. Cársky, M. Urban: Ab Initio Calculations. Methods and Applications in Chemistry. Lecture Notes in Chemistry, Vol. 18. Springer-Verlag, Berlin 1980, 247 p.

Czech edition: Ab initio výpocty v chemii. SNTL, Praha 1985, 279 p. J. Paldus contributed numerous Chapters to various monographs and is currently on several Editorial Boards (in particular for a book series "Advances in Quantum Chemistry" published by Academic Press).