The step-size in standard MD is restricted by the high-frequency bond vibrations whereas the interesting conformational changes occur over much longer time-scales. Several methods to increase the step-size have been proposed. Roughly, those methods belong to either one of the following two categories: (i) implicit or semi-implicit methods and (ii) reduced equations of motion in torsion space or some other ''essential'' subspace. In this talk, we show by means of toy problems, that approach (i) will almost always lead to qualitatively erroneous results while approach (ii) leads to nontrivial considerations concerning an appropriate derivation of the reduced equations of motion. Mathematically these questions are closely tied to various averaging concepts such as time and ensemble averages and the formulation of corresponding correcting potentials for the reduced equations of motion.
Sebastian Reich
Konrad-Zuse-Zentrum
Berlin, Germany
