These two volumes collect thirty-eight selected papers from the scientific contributions presented at the Fourth European Workshop on Quantum Systems in Chemistry and Physics (QSCP-IV), held in Marly-le-Roi (France) in April 22-27, 1999. A total of one hundred and fifteen scientists attended the workshop, 99 from Europe and 16 from the rest of the world. They discussed the state of the art, new trends, and future evolution of the methods and applications. The workshop was held in the old town of Marly-le-Roi, which lies to the West of Paris between the historic centres of Saint-Germain-en-Laye and Versailles. Participants were housed at the National Youth Institute, where over sixty lectures were given by l- ding members of the scientific community; in addition, over sixty posters were presented in two very animated sessions. We are grateful to the oral speakers and to the poster p- senters for making the workshop such an stimulating experience. The social programme was also memorable and not just for the closing banquet, which was held at the French Senate House. We are sure that participants will long remember their visit to the 'Musée des Antiquités Nationales': created by Napoleon III at the birthplace of Louis XIV, this museum boasts one of the world finest collections of archeological artifacts. The Marly-le-Roi workshop followed the format established at the three previous meetings, organized by Prof.

Inhalt
Response Theory: Properties and Spectra.- On Gauge Invariance and Molecular Electrodynamics.- Quantum Mechanics of Electro-Nuclear Systems Towards a Theory of Chemical Reactions.- Theoretical Study of Regularities in Atomic and Molecular Spectral Properties.- Excited States of Hydrogen Peroxide: An Overview.- On Electron Dynamics in Violent Cluster Excitations.- Relativistic Effects in Non-Linear Atom-Laser Interactions at Ultrahigh Intensities.- Reactive Collisions and Chemical Reactions.- Semiclassical Close-Coupling Description of Electron Transfer in Multicharged Ion-Atom Collisions.- Single and Double Electron Capture in Boron Collision Systems.- Theoretical Study of the Interaction of Carbon Dioxide with Sc, Ti, Ni, and Cu Atoms.- Condensed Matter.- Recurrent Variational Approach Applied to the Electronic Structure of Conjugated Polymers.- Effects of Solvation for (R,R) Tartaric-Acid Amides.- Interpretation of Vibrational Spectra in Electrochemical Environments from First-Principle Calculations: Computational Strategies.- Excited States in Metal Oxides by Configuration Interaction and Multireference Perturbation Theory.- Electrostatic Effects in the Heterolytic Dissociation of Hydrogen at Magnesium Oxide.- A DFT Study of CO Adsorption on NiII Ions 3-Fold Coordinated to Silica.- A Theoretical Study of Structure and Reactivity of Titanium Chlorides.- Phenomenological Description of D-Wave Condensates in High-Tc Superconducting Cuprates.