# Quantitative Predictions of Photoelectron Spectra in Amorphous Molecular Solids from Multiscale Quasiparticle Embedding

## TL;DR

This paper introduces a multiscale first-principles simulation framework that accurately predicts ultraviolet photoelectron spectra of amorphous molecular solids, aiding in the precise determination of HOMO energies crucial for organic electronics.

## Contribution

The novel multiscale approach combines deposition simulation, Green's Function Theory, and vibrational coupling to bridge experimental and theoretical spectral analysis of amorphous materials.

## Key findings

- Excellent agreement with experimental spectra of MADN is achieved.
- HOMO energies can be determined with an accuracy better than 0.1 eV.
- The method provides molecular-level insights into spectral features.

## Abstract

We present a first-principles-based multiscale simulation framework for quantitative predictions of the high-energy part of the Ultraviolet Photoelectron Spectroscopy (UPS) spectra of amorphous molecular solids. The approach combines a deposition simulation, many-body Green's Function Theory, polarizable film-embedding, and multimode electron-vibrational coupling and provides a molecular-level view on the interactions and processes giving rise to spectral features. This insight helps bridging the current gap between experimental UPS and theoretical models as accurate analyses are hampered by the energetic disorder, surface-sensitivity of the measurement and the complexity of excitation processes. In particular this is relevant for the unambiguous determination the highest occupied molecular orbital energy (HOMO) of organic semiconductors, a key quantity for tailoring and engineering new opto-electronic devices. We demonstrate the capabilities of the simulation approach studying the spectrum of two isomers of 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as archetypical materials showing a clearly separated HOMO peak in experiment. The agreement with experiment is excellent, suggesting that our approach provides a route for determining the HOMO energy with an accuracy better than 0.1eV.