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.

Today, coupled-cluster (CC) theory has emerged as the most accurate, widely applicable approach for the correlation problem in molecules. Furthermore, the correct scaling of the energy and wavefunction with size (i.e. extensivity) recommends it for studies of polymers and crystals as well as molecules. CC methods have also paid dividends for nuclei, and for certain strongly correlated systems of interest in field theory.In order for CC methods to have achieved this distinction, it has been necessary to formulate new, theoretical approaches for the treatment of a variety of essential quantities. These include properties and, particularly, analytical first derivatives (gradients) that readily provide the forces on the atoms in a molecule to facilitate searching potential energy surfaces for structures and transition states; second derivatives (Hessians) which indicate the type of extremum point and provide vibrational frequencies and intensities; excited, ionized, and electron attached states including their properties; multi-configurational reference functions to add important non-dynamic correlation; and relativistic effects.This book addresses very recent work in each of the above topics in ten chapters written by leading experts in molecular CC theory. This is NOT a collection of reviews, but is, instead, forefront research explained in an unusually clear exposition. Each chapter presents new results and formulations that offer another step toward providing the next generation of powerful CC solutions.The gap that often exists between text books and research can be more of a chasm in highly technical fields like CC theory, but this volume helps to fill the void, as it provides a sequel to a graduate level course in CC theory and many-electron methods. Essentially all current directions for new research are well represented in the authoritative articles.

Modern Electronic Structure Theory provides a didactically oriented description of the latest computational techniques in electronic structure theory and their impact in several areas of chemistry. The book is aimed at first year graduate students or college seniors considering graduate study in computational chemistry, or researchers who wish to acquire a wider knowledge of this field.

Quantum many-body theory as a discipline in its own right dates largely from the 1950's. It has developed since then to its current position as one of the cornerstones of modern theoretical physics. The field remains vibrant and active, vigorous and exciting. Its most powerful techniques are truly universal. They are constantly expanding to find new fields of application, while advances continue to be made in the more traditional areas. To commemorate the impending 80th birthdays of its two co-inventors, Firtz Coester and Hermann Kummel, one such technique, namely the coupled cluster method, was especially highlighted at this meeting, the eleventh in the series of International Conferences on Recent Progress in Many-Body Theories. The history of the coupled cluster method as told here mirrors in many ways both the development of the entire discipline of microscopic quantum many-body theory and the history of the series of conferences. The series itself is universally recognised as being the premier series of meetings in this subject area. Its proceedings have always summarised the current state of the art through the lectures of its leading practitioners. The present volume is no exception. No serious researcher in quantum many-body theory or in any field which uses it can afford to be without this volume.

This conference series is now firmly established as one of the premier series of international meetings in the field of many-body physics. The current volume maintains the tradition of covering the entire spectrum of theoretical tools developed to tackle important and current quantum many-body problems. It aims to foster the exchange of ideas and techniques among physicists working in diverse subfields of physics, such as nuclear and sub-nuclear physics, astrophysics, atomic and molecular physics, quantum chemistry, complex systems, quantum field theory, strongly correlated electronic systems, magnetism, quantum fluids and condensed matter physics. The highlights of this book include state-of-the-art contributions to the understanding of supersolid helium, BEC-BCS crossover, fermionic BEC, quantum phase transitions, computing, simulations, as well as the latest results on the more traditional topics of liquid helium, droplets, nuclear and electronic systems. This volume demonstrates the vitality and the fundamental importance of many-body theories, techniques, and applications in understanding diverse and novel phenomena at the cutting-edge of physics. It contains most of the invited talks plus a selection of excellent poster presentations.

This volume brings together selected contributed papers presented at the International Conference of Computational Methods in Science and Engineering (ICCMSE 2006), held in Chania, Greece, October 2006. The conference aims to bring together computational scientists from several disciplines in order to share methods and ideas. The ICCMSE is unique in its kind. It regroups original contributions from all fields of the traditional Sciences, Mathematics, Physics, Chemistry, Biology, Medicine and all branches of Engineering. It would be perhaps more appropriate to define the ICCMSE as a conference on computational science and its applications to science and engineering. Topics of general interest are: Computational Mathematics, Theoretical Physics and Theoretical Chemistry. Computational Engineering and Mechanics, Computational Biology and Medicine, Computational Geosciences and Meteorology, Computational Economics and Finance, Scientific Computation. High Performance Computing, Parallel and Distributed Computing, Visualization, Problem Solving Environments, Numerical Algorithms, Modelling and Simulation of Complex System, Web-based Simulation and Computing, Grid-based Simulation and Computing, Fuzzy Logic, Hybrid Computational Methods, Data Mining, Information Retrieval and Virtual Reality, Reliable Computing, Image Processing, Computational Science and Education etc. More than 800 extended abstracts have been submitted for consideration for presentation in ICCMSE 2005. From these 500 have been selected after international peer review by at least two independent reviewers.

Coupled-cluster theory in its single-reference formulation represents one of the most successful approaches in quantum chemistry for the description of atoms and molecules. To extend the applicability of single-reference coupled-cluster theory to systems with degenerate or near-degenerate electronic configurations, multireference coupled-cluster methods have been suggested. One of the most promising formulations of multireference coupled cluster theory is the state-specific variant suggested by Mukherjee and co-workers (Mk-MRCC). Unlike other multireference coupled-cluster approaches, Mk-MRCC is a size-extensive theory and results obtained so far indicate that it has the potential to develop to a standard tool for high-accuracy quantum-chemical treatments. This work deals with developments to overcome the limitations in the applicability of the Mk-MRCC method. Therefore, an efficient Mk-MRCC algorithm has been implemented in the CFOUR program package to perform energy calculations within the singles and doubles (Mk-MRCCSD) and singles, doubles, and triples (Mk-MRCCSDT) approximations. This implementation exploits the special structure of the Mk-MRCC working equations that allows to adapt existing efficient single-reference coupled-cluster codes. The algorithm has the correct computational scaling of d*N^6 for Mk-MRCCSD and d*N^8 for Mk-MRCCSDT, where N denotes the system size and d the number of reference determinants. For the determination of molecular properties as the equilibrium geometry, the theory of analytic first derivatives of the energy for the Mk-MRCC method has been developed using a Lagrange formalism. The Mk-MRCC gradients within the CCSD and CCSDT approximation have been implemented and their applicability has been demonstrated for various compounds such as 2,6-pyridyne, the 2,6-pyridyne cation, m-benzyne, ozone and cyclobutadiene. The development of analytic gradients for Mk-MRCC offers the possibility of routinely locating minima and transition stat.