Monte Carlo algorithm based on internal bridging moves for the atomistic simulation of thiophene oligomers and polymers

TL;DR

This paper presents a novel Monte Carlo algorithm tailored for atomistic simulations of thiophene oligomers and polymers, enabling efficient exploration of their phase behavior and nanoscale ordering beyond the capabilities of traditional molecular dynamics methods.

Contribution

The authors adapt and extend Monte Carlo moves originally for simpler polymers to accurately simulate the complex ring structure of thiophenes, facilitating studies of long-chain polymer phase behavior.

Findings

Predictions closely match detailed atomistic MD simulations.

Algorithm effectively captures volumetric and conformational properties.

Promising for exploring phase transitions in long thiophene polymers.

Abstract

We introduce a powerful Monte Carlo (MC) algorithm for the atomistic simulation of bulk models of oligo- and poly-thiophenes by redesigning MC moves originally developed for considerably simpler polymer structures and architectures, such as linear and branched polyethylene, to account for the ring structure of the thiophene monomer. Elementary MC moves implemented include bias reptation of an end thiophene ring, flip of an internal thiophene ring, rotation of an end thiophene ring, concerted rotation of three thiophene rings, rigid translation of an entire molecule, rotation of an entire molecule and volume fluctuation. In the implementation of all moves we assume that thiophene ring atoms remain rigid and strictly co-planar; on the other hand, inter-ring torsion and bond bending angles remain fully flexible subject to suitable potential energy functions. Test simulations with the new algorithm of an important thiophene oligomer, {\alpha}-sexithiophene ({\alpha}-6T), at a high enough temperature (above its isotropic-to-nematic phase transition) using a new united atom model specifically developed for the purpose of this work provide predictions for the volumetric, conformational and structural properties that are remarkably close to those obtained from detailed atomistic Molecular Dynamics (MD) simulations using an all-atom model. The new algorithm is particularly promising for exploring the rich (and largely unexplored) phase behavior and nanoscale ordering of very long (also more complex) thiophene-based polymers which cannot be addressed by conventional MD methods due to the extremely long relaxation times characterizing chain dynamics in these systems.