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

Recent developments that increase the time and distance scales accessible i n the simulations of specific polymers are reviewed. Several different tech niques are similar in that they replace a model expressed in fully atomisti c detail with a coarse-grained model of the same polymer, atomistic --> coa rse-grained land beyond!), thereby increasing the time and distance scales accessible within the expenditure of reasonable computational resources. Th e bridge represented by the right-pointing arrow can be constructed via dif ferent procedures, which are reviewed here. The review also considers the s tatus of methods which reverse this arrow, atomistic <-- coarse-grained. Th is "reverse-mapping" recovers a model expressed in fully atomistic detail f rom an arbitrarily chosen replica generated during the simulation of the co arse-grained system. Taken in conjunction with the efficiency of the simula tion when the system is in its coarse-grained representation, the overall p rocess 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 p ermits a much more complete equilibration of the system (larger effective s ize of Delta t) when that equilibration is performed with the coarse-graine d replicas (II --> III) than if it were attempted with the fully atomistic replicas (I --> IV).