Electronic polarization at surfaces and thin films of organic molecular crystals: PTCDA

TL;DR

This paper calculates electronic polarization energies in PTCDA thin films on metals, showing a significant increase in polarization in monolayers compared to thicker films, aligning theory with experimental transport gap measurements.

Contribution

It introduces a self-consistent method to compute electronic polarization energies at surfaces and interfaces of organic crystals, specifically applied to PTCDA on metallic substrates.

Findings

Polarization energy is 500 meV larger in monolayers than in 50 Å films.

Theoretical calculations agree with experimental measurements of the transport gap.

Electronic polarization is obtained via charge redistribution within molecules.

Abstract

The electronic polarization energies, P = (P+) + (P-), of a PTCDA (perylenetetracarboxylic acid dianhydride) cation and anion in a crystalline thin film on a metallic substrate are computed and compared with measurements of the PTCDA transport gap on gold and silver. Both experiments and theory show that P is 500 meV larger in a PTCDA monolayer than in 50 A films. Electronic polarization in systems with surfaces and interfaces are obtained self-consistently in terms of charge redistribution within molecules.