The quantum mechanical description rests on the Density Functional Theory, for which Walter Kohn was awarded the Nobel prize in Chemistry in 1998. The ab-initio molecular dynamics approach developed by Roberto Car and Michele Parrinello provides movies of the atomic motion at finite temperatures or during a chemical reaction. In the department we use the CP-PAW program-package developed by P.E. Blöchl and his colaborators, which is maintained and distributed by the department. The Projector augmented-wave (PAW) method invented by Peter Blöchl is an accurate and efficient all-electron electronic structure method for large systems and dynamical studies.