By Eugene S. Kryachko
I need to provide to a large circle of the readers operating in quantum chem istry and solid-state physics, as, .ell as in different fields of many-body physics and its interfaces, this e-book deyoted to density useful conception written via my colleagues Eugene S. Kryachko and Eduardo Y. Ludena. Their how one can this thought are relatively varied even though essentially either one of them are quantum chemical. Eugene S. Kryachko got here to strength density sensible thought from the idea of lowered density matrices, and Eduardo \'. Ludena dewloped previous the idea that of loges in quantum chemistry. Neyertheless, their previous pursuits giw the prospect to consolidate and formulate strength density practical concept in a unified and constant means, for my part. Raymond Daudel Paris ACKNOWLEDGMENTS The authors are indebted to Carl Almbladh, Victor Va. Antonchenko, John Avery, Richard F. W. Bader, Ulf \'on Barth, Jean-Louis Calais, A. John Coleman, Jens P. Dahl, Robert Donnelly, Harold Englisch, Robert 1\1. Erdahl, Oswaldo Goscinski, John E. Harriman, Gintas Kamuntavichius, Illja G. Kaplan, Jaime Keller, \'alentin Khart siev, Toshikatsu Koga, Per-Olov Lo\ydin, T. Tung Nguyen-Dang, Ivan Zh. Petkov, Jerome ok. Percus, l\lary Beth Ruskai, John R. Sabin, Zdenek Slanina, \'ladimir Shi rokov, l\lario V. Stoitsov, Yoram Tal, and \Vaitao Yang, who in a single manner or one other, both via their sort aid, support, discussions or priceless reviews created the human and highbrow history which made this booklet attainable.