Mixing atoms and coarse-grained beads in modelling polymers

The scope of this chapter is to give an overview of the different types of dual-resolved models for the simulation of molecular systems, with some emphasis on the application to macromolecules, employing a mixed atomistic/coarse-grained resolution. Dual-resolved models gained some traction because they combine the advantages of two resolutions (generally, atomistic and coarse-grained) while trying to overcome their respective limitations. In particular, by coarse-graining a region of the system, we are able to leverage the computational efficiency of coarse-grained simulations and at the same time, by describing one or a few regions of the molecules at the atomistic level, we are able to limit the loss of information inherent in the CG models by retaining the chemical detail only in the portion of the system we are most interested in. Here, we describe the two main classes of approach to dual-resolved methods, namely the static and the dynamic one. In the former, the resolution of the various system parts is assigned beforehand and kept fixed during all the simulation, while in the latter the regions described at the atomistic level may change over time in the course of the simulation. We provide an overview of such models and discuss in which direction the field is moving, starting from its recent history and the related literature covering the past few decades.