Quantum-mechanical calculations based on density functional theory

The basic concepts of density functional theory (DFT) together with the local density approximation (LDA) and the recent improvement in form of the generalized gradient approximations (GGA) are discussed. Band structure calculations using the full-potential linearized augmented plane wave (FP-LAPW) method are presented in relation to pseudopotential schemes both corresponding to T=0. For finite temperatures the most advanced technique is the Car-Parrinello (CP) molecular dynamics (MD) approach, e.g. in its projector augmented wave (PAW) implementation. In CP-MD simulations nuclear motion and the electronic degrees of freedom are treated within one formalism. Such DFT calculations are illustrated for selected examples, including the breathing mode of BaBiO₃. the phase transition in SrTiO₃ and VO₂ and the Li diffusion in the superionic conductor Li₃N studied by conventional and CP molecular dynamics.