Bridging the gap between atomistic and coarse-grained models of polymers:: Status and perspectives

Recent developments that increase the time and distance scales accessible in the simulations of specific polymers are reviewed. Several different techniques are similar in that they replace a model expressed in fully atomistic detail with a coarse-grained model of the same polymer, atomistic --> coarse-grained land beyond!), thereby increasing the time and distance scales accessible within the expenditure of reasonable computational resources. The bridge represented by the right-pointing arrow can be constructed via different procedures, which are reviewed here. The review also considers the status of methods which reverse this arrow, atomistic <-- coarse-grained. This "reverse-mapping" recovers a model expressed in fully atomistic detail from an arbitrarily chosen replica generated during the simulation of the coarse-grained system. Taken in conjunction with the efficiency of the simulation when the system is in its coarse-grained representation, the overall process I. Atomistic, t(O) --> II. Coarse - grained, t(O) abc IV. Atomistic, t(O)+t <-- III. Coarse - grained, t(O) + t down arrow V. Semimacroscopic permits a much more complete equilibration of the system (larger effective size of Delta t) when that equilibration is performed with the coarse-grained replicas (II --> III) than if it were attempted with the fully atomistic replicas (I --> IV).