Classical Force Fields and Methods of Molecular Dynamics

The practical size and time scale for QM based MD (QM-MD or AIMD) is 200 atoms for 50 ps. But we want to do MD on systems with 100,000 to 3 million atoms for 100's of ns. Thus the forces from QM must be replaced for analytic functions that depend directly on distances and angles. The parameters could be trained with QM but better is to develop rules that lead to an acceptable accuracy for wide classes of materials. Thus we developed DREIDING for main group elements (columns 14–17) and later UFF for all elements (up to Lr, Z=103) aimed at inorganic materials. These are aimed at structures but not bond breaking. For bond breaking we developed the ReaxFF and RexPoN FF described in chapter 47.