Protracted Colored Noise Dynamics in Atomically Detailed Simulations

Sampling the conformation space of high molecular weight polymers in simulations is challenging because their high viscosities make them rearrange very slowly, causing molecular dynamics (MD) simulations of these polymer systems to take an extremely long time. To improve the efficiency of these simulations, Protracted Colored-Noise Dynamics (PCND) adds additional stochastic forces to MD simulations to artificially increase the movement and diffusivity of molecules. Recently, the PCND method has been applied to polymer systems by adding these forces along the polymer chain contour, and preliminary results indicate that the chain diffusivity is increased in simple meso-scale polymer models of block copolymers. We have applied this method to simple polymers in atomistic detail (polyethylene) to determine its effectiveness for atomically detailed polymers. Our results for bulk systems were nearly equivocal and did not show significant increases in the polymer's ability to sample a variety of conformations, possibly because we did not apply the method in the optimal range of the PCND parameter space. We then simulated single polymer chains to verify that the method was working properly, and in these simulations PCND was obviously superior in sampling a broader distribution of the conformation space. These results give us more reason to hope that this method can speed up bulk simulations of atomically detailed polymers once the optimal range of the PCND parameter space is found.