Electronic Correlations in Oligo-acene and -thiophene Organic Molecular Crystals

TL;DR

This paper uses first principles calculations to analyze how electron-electron interactions in oligo-acene and -thiophene crystals influence their electronic properties, especially under high doping conditions.

Contribution

It provides a detailed quantification of Coulomb interactions and polarization effects in organic molecular crystals, highlighting the significance of correlations at high doping levels.

Findings

Electronic polarization reduces Coulomb repulsion by about half.

Effective hole-hole repulsion exceeds valence bandwidth.

Correlations dominate the electronic properties at high doping.

Abstract

From first principles calculations we determine the Coulomb interaction between two holes on oligo-acene and -thiophene molecules in a crystal, as a function of the oligomer length. The relaxation of the molecular geometry in the presence of holes is found to be small. In contrast, the electronic polarization of the molecules that surround the charged oligomer, reduces the bare Coulomb repulsion between the holes by approximately a factor of two. In all cases the effective hole-hole repulsion is much larger than the calculated valence bandwidth, which implies that at high doping levels the properties of these organic semiconductors are determined by electron-electron correlations.