DFT Embedding and Coarse Graining Techniques

Classical molecular dynamics and first principles quantum mechanical calculations are two of the most important methods currently used to model physical systems at the atomic level. The former allow simulations of millions of atoms to be carried out on a nanosecond timescale but the accuracy is limited by the requirement to use simple parameterisations as interatomic potentials. If the scientific question of interest can be effectively answered by considering the behaviour of a very small number of atoms, up to around a hundred, then ab initio approaches allow this limitation to be overcome. In many cases we can extract enough information from these accurate quantum mechanical calculations to parameterise less transferable, but far less expensive, models and use them on a larger length scale. For some systems however, it is impossible to separate the behaviour on the various length scales, since the coupling between them is strong and bidirectional. Then the only option is to carry out a hybrid simulation, where some parts of the system are treated at a higher level of accuracy; this is the subject of this lecture.