This is one of two volumes which together comprise 40 papers coming from the most outstanding contributions to the third European Quantum Systems in Chemistry and Physics Workshop held in Granada, Spain (1997). These books cover a spectrum of scientific research from quantum-mechanical many-body methods to important applications and computational developments, and from atoms and molecules to condensed matter. The first volume is subtitled "Basic Problems and Model Systems", and includes the following topics: density matrices and density functionals, electron correlation effects, relativistic formulations, valence theory, and nuclear motions. The second volume is subtitled "Advanced Problems and Complex Systems" and covers the following topics: response theory, condensed matter, reactive collisions and chemical reactions and computational chemistry and physics.