Does the total energy difference method for modelling core level photoemission fail for bigger molecules?

TL;DR

This study reassesses the $ ext{Δ}$SCF method for core electron binding energies, showing it remains accurate for larger molecules and extended systems, contrary to prior reports of failure.

Contribution

The paper demonstrates that the $ ext{Δ}$SCF method is effective for medium to large molecules, supported by new experimental data and comprehensive benchmarking.

Findings

New experimental C 1s binding energies for anthrone align with $ ext{Δ}$SCF calculations.

The mean absolute error for 44 molecules is 0.19 eV, comparable to previous benchmarks.

$ ext{Δ}$SCF performs well for localized excitations in larger molecules.

Abstract

The $\Delta$-Self-Consistent-Field ($\Delta$SCF) method permits calculations of core electron binding energies in materials and molecules at a modest computational cost. However, it has been reported that whilst this method works well for small molecules, its accuracy drops off dramatically when larger systems are considered. Particularly large errors have been reported for the anthrone molecule, which consists of 25 atoms. In this work, the gas-phase photoelectron spectrum of anthrone is revisited both computationally and experimentally. The measured C 1s binding energies in anthrone differ markedly from previously published values, and the new experimental results are in good agreement with $\Delta$SCF calculations based on the SCAN functional. In addition, the performance of the $\Delta$SCF method is evaluated for a dataset of 44 core electron binding energies from medium sized molecules containing between 10 and 40 atoms. The mean absolute error for this dataset - 0.19 eV - is comparable to the results of previous computational benchmarks. Overall, these results and general theoretical considerations indicate that the $\Delta$SCF method is suitable for modelling localized excitations in both small and large molecules, and applications to other extended systems are also promising.