Monte Carlo simulation of tetrahedral chains, 5. The pivot‐algorithm for non‐athermal linear and star‐branched polymers

Abstract

AbstractBy use of the pivot algorithm, star‐branched chains with F = 3–12 arms of length n, nF = 480, and linear chains (F = 2) are generated on a tetrahedral lattice. In order to simulate different qualities of the solvent, specific short‐range interactions are taken into account. Whereas in athermal systems a new configuration — which is obtained by rotating that part of an arm which contains the chain end around a randomly selected bond by ± 120° — is accepted if it is self‐avoiding, for non‐athermal systems the Metropolis‐Rosenbluth criterion with respect to energy must be satisfied in addition. Calculating the energy of the configuration, nearest‐neighbour interactions (each contact contributes an energy Φ·kT, Φ < 0 characterizing endothermal solutions and Φ > 0 exothermal ones) are considered only; no energy is introduced to distinguish between trans and gauche bonds. A rather quick response of chain properties to the variation of thermodynamic conditions is demonstrated. The average acceptance fraction f̄ has its maximum value for athermal conditions, slightly decreases for exothermal conditions and strongly decreases with increasingly negative Φ‐values. However, for Φ = −0,5 — representing a solution near theta‐conditions — still 25% of attempted moves are accepted for all F‐values examined. The dependence of global properties (characterized by the mean‐square radius of gyration) on Φ and F is in full accordance with most Monte Carlo results.