This volume contains all of the invited lectures presented at the NATO ARWon "New Methods in Quantum Theory" held in Halkidiki, Greece from May 14th to May 19th, 1995. This survey of new perspectives, techniques and results in quantum theory contains 26 chapters by leading quantum chemists and physicists from 14 countries. The book covers a wide range of topics, though the emphasis throughout is on new approaches and their interrelationships. Topics covered include dimensional scaling, the hyperspherical method applied both to reactive scattering theory and to bound state problems, chaotic behaviour, large-order perturbation theory, complex eigenvalues and quasistationary states, semiclassical methods, cusps in hyperaccurate wave functions, density functional theory, relativistic quantum theory, and quantum Monte Carlo methods. I hope very much that the various lectures presented at this Advanced Research Workshop will be of as great interest to the reader as they were to the participants. The organization of the ARW would have been impossible without the generous funding by NATO, which is gratefully acknowledged. I sincerely thank Drs. J. -M. Cadiou, Assistant Secretary General for Scientific and Environmental Affairs, and J. A. Rausell-Colom, Programme Director for Priority Area on High Technology, North Atlantic Treaty Organization, who helped me throughout the various stages of the ARW.

Dimensional scaling offers a new approach to quantum dynamical correlations. This is the first book dealing with dimensional scaling methods in the quantum theory of atoms and molecules. Appropriately, it is a multiauthor production, derived chiefly from papers presented at a workshop held in June 1991 at the A~rsted Institute in Copenhagen. Although focused on dimensional scaling, the volume includes contributions on other unorthodox methods for treating nonseparable dynamical problems and electronic correlation. In shaping the book, the editors serve three needs: an introductory tutorial for this still fledgling field; a guide to the literature; and an inventory of current research results and prospects. Part I treats basic aspects of dimensional scaling. Addressed to readers entirely unfamiliar with the subject, it provides both a qualitative overview, and a tour of elementary quantum mechanics. Part II surveys the research frontier. The eight chapters exemplify current techniques and outline results. Part III presents other methods, including nonseparable dynamics, and electron correlation in pseudomolecular excited states of atoms. Although procrustean conformity was not imposed, unifying and complementary themes are emphasized throughout the book.

Dimensional scaling offers a new approach to quantum dynamical correlations. This is the first book dealing with dimensional scaling methods in the quantum theory of atoms and molecules. Appropriately, it is a multiauthor production, derived chiefly from papers presented at a workshop held in June 1991 at the A~rsted Institute in Copenhagen. Although focused on dimensional scaling, the volume includes contributions on other unorthodox methods for treating nonseparable dynamical problems and electronic correlation. In shaping the book, the editors serve three needs: an introductory tutorial for this still fledgling field; a guide to the literature; and an inventory of current research results and prospects. Part I treats basic aspects of dimensional scaling. Addressed to readers entirely unfamiliar with the subject, it provides both a qualitative overview, and a tour of elementary quantum mechanics. Part II surveys the research frontier. The eight chapters exemplify current techniques and outline results. Part III presents other methods, including nonseparable dynamics, and electron correlation in pseudomolecular excited states of atoms. Although procrustean conformity was not imposed, unifying and complementary themes are emphasized throughout the book.