Adaptive Resolution Simulations: Towards Open Systems Molecular Dynamics Simulations
Kurt Kremer (Max Planck Institute for Polymer Research)

The relation between atomistic structure, architecture, molecular weight and material properties is a basic concern of modern soft matter science. This longstanding aim by now goes far beyond standard properties of bulk materials. A typical additional focus is on surface interface aspects or the relation between structure and function in nanoscopic molecular assemblies This all implies a thorough understanding on many length and correspondingly time scales ranging from (sub)-atomic to macroscopic. Traditionally computer simulations have been separated in two main groups, namely simplified models to deal with generic or universal aspects, i.e. critical exponents, of polymers and those employing classical force field simulations with (almost) all atomistic detail, i.e. for the diffusion of small additives in small “sample”. To progress further adaptive schemes have to be developed, which allow for a free exchange of particles (atoms, molecules) between the different levels of resolution. First attempts towards this direction will be presented in this lecture. We study model systems, which display a spatially variable resolution with a free exchange of particles between the different regimes, ranging from atomistic resolution to coarse grained and continuum.

The new scheme can be understood within a (very limited analogy) to a geometry induced phase transition, where in the transition regime degrees of freedom are switched on or off. Theoretically one can formulate this in terms of fractional degrees of freedom. This methodology has been tested for methane like tetrahedral liquids, polymers in solution as well as liquid water.

M. Praprotnik, L. Delles Site, K. Kremer „Adaptive Resolution Molecular Dynamics Simulation: Changing the Degrees of Freedom on the Fly” J. Chem. Phys. *123 *(2005)
M. Praprotnik, S. Matysiak, L. Delle Site, K. Kremer, C. Clementi, Adaptive Resolution Simulation of Liquid Water“, J. Phys. Cond. Matt. *19,* 292201 (2007)
N.F.A. van der Vegt, C. Peter, and K. Kremer, Structure-based coarse- and fine-graining in soft matter simulations, In Coarse-Graining of Condensed Phase and Biomolecular Systems, ed. G.A. Voth, Chapman and Hall/CRC Press, Taylor and Francis Group, 2008
M. Praprotnik, L. Delle Site, and K. Kremer, Multiscale Simulation of Soft Matter: From Scale Bridging to Adaptive Resolution, Annu. Rev. Phys. Chem. *59*, (2008).