A simplified picture for Pi electrons in conjugated polymers : from PPP Hamiltonian to an effective molecular crystal approach

TL;DR

This paper introduces an excitonic method for studying conjugated polymers, deriving an effective Hamiltonian from the PPP model to simplify analysis of electronic states and absorption spectra.

Contribution

It presents a new excitonic approach based on a local monomer description, simplifying the analysis of conjugated polymers from the PPP Hamiltonian.

Findings

Effective Hamiltonian derived from PPP model for conjugated polymers.

Linear absorption dominated by an intense excitonic peak.

Model successfully applied to trans-polyacetylene.

Abstract

An excitonic method proper to study conjugated oligomers and polymers is described and its applicability tested on the ground state and first excited states of trans-polyacetylene, taken as a model. From the Pariser-Parr-Pople Hamiltonian, we derive an effective Hamiltonian based on a local description of the polymer in term of monomers; the relevant electronic configurations are build on a small number of pertinent local excitations. The intuitive and simple microscopic physical picture given by our model supplement recent results, such as the Rice and Garstein ones. Depending of the parameters, the linear absorption appears dominated by an intense excitonic peak.