Ionization potentials of crystalline organic thin films: Position dependence due to molecular shape and charge redistribution

TL;DR

This study investigates how molecular shape and charge redistribution influence the position-dependent ionization potentials in crystalline organic thin films, highlighting the significance of charge-quadrupole interactions across different molecular layers.

Contribution

It introduces a computational approach to quantify the impact of molecular shape on ionization potentials in organic thin films, emphasizing the role of charge-quadrupole interactions.

Findings

Shape effects can cause up to 0.5 eV variation in ionization potentials.

Charge-quadrupole interactions are the primary cause of shape-dependent energy shifts.

Depth dependence of ionization potential varies among different organic molecules.

Abstract

In addition to electronic polarization or charge redistribution, the shape of neutral conjugated molecules yields position-dependent ionization potentials and electron affinities in organic thin films. Self-consistent I(n) and A(n) are computed in each layer n of 10-layer films of prototypical organics on a metal. The depth dependence of I(n) is discussed at surfaces of anthracene, C60 and PTCDA. The shape contribution can be substantial, up to 0.5 eV, and comes primarily from charge-quadrupole interactions.