# Simulation of Charge Distribution and Microstructure in Semicrystalline Polymeric Ionic-Electronic Conductors Using Classical Simulation at Constant Electrochemical Potential

## TL;DR

This paper introduces a new simulation method to study how charge and structure change in polymer materials under constant electrochemical conditions.

## Contribution

A novel classical simulation framework for studying charge distribution and microstructure in doped polymers under constant electrochemical potential.

## Key findings

- The method reproduces minimal structural changes in semicrystalline polymers under varying electrochemical potentials.
- Near the redox potential, charging levels fluctuate more and interlamellar angles vary significantly.
- Local charge correlations between polymer chains are minimal except at extreme potentials.

## Abstract

Understanding how charge distributions on aggregated
chains change
with microstructure under constant electrochemical potential is crucial
for elucidating the behavior of polymeric organic mixed ionic–electronic
conductors (OMEICs), yet it remains difficult to study. To address
this challenge, we introduce a methodology to perform classical atomistic
simulations of doped semiconductors at a constant electrochemical
potential. The method allows individual polymer chains to be oxidized
and reduced, taking into account their individual redox potentials
and the externally tunable electrochemical potential. The implementation
follows a grand-canonical molecular dynamics (GC-MD) scheme, with
the local modulation of the redox potential being described by a QM/MM
Hamiltonian. Applied to a semicrystalline polymer with ordered layered
and lamellar structures, the method reproduces the experimentally
observed minimal structural changes over the electrochemical potentials
and charging levels considered. Near the redox potential, charging
levels fluctuate more strongly, and variations in the interlamellar
angle (defined by the normal of adjacent lamellae) are most pronounced.
Moreover, analysis of the local environment reveals no detectable
correlation between a chain’s redox reaction and the charge
distribution of neighboring chains, except at the most negative potentials,
where redox events occur preferentially in more positively charged
surroundings. Lastly, examination of individual chains shows minimal
chain–chain charge correlation, and the single-chain conformation
remains closely linked to its redox behavior. Overall, this work provides
a robust framework for investigating charge distributions in dynamically
doped systems and offers new conceptual routes for studying polymer
structural responses under constant electrochemical potentials.