Extended continuum configurational bias Monte Carlo methods for simulation of flexible molecules

Abstract

The continuum configurational bias (CCB) Monte Carlo method has been extended to perform elementary moves that involve the rearrangement of inner segments of flexible chains. When regrowing inner sites, the continuity with the rest of the chain is ensured by disregarding those configurations that would imply an unrealistic elongation of the bonds once the chain is reconstructed. The formalism presented here also allows the simulation of branched chains and crosslinked-network structures. The Monte Carlo elementary moves proposed in this work are used in conjunction with an alternative method of preferential sampling in which the segments to be rearranged are chosen from a preselected region of space. The performance and capabilities of the new moves are compared to those of standard CCB and crank-shaft algorithms for simulation of melts and solutions of hard-sphere chains at high densities. Our results indicate that the methods presented here provide a fast relaxation of the bond orientation and the end-to-end orientation autocorrelation functions. Our isobaric simulations for homopolymer chains of up to 51 sites and for concentrated solutions of chain molecules in the monomer are consistent with previously reported data obtained by approximate molecular dynamics methods and by conventional Monte Carlo methods. However, small disagreements with existing data are identified at high densities. These PV results are also compared to the predictions of two recent equations of state. This comparison shows the presence of some small but systematic deviations.