Towards an ab initio theory for metal L-edge soft X-ray spectroscopy of molecular aggregates

TL;DR

This paper develops an efficient ab initio approach using the Frenkel exciton model and restricted active space methods to simulate metal L-edge X-ray spectra of molecular aggregates, reducing computational costs while capturing aggregation effects.

Contribution

It introduces a novel computational protocol combining the Frenkel exciton model with RASSCF to accurately simulate X-ray spectra of transition metal complexes with lower resource requirements.

Findings

Aggregation effects are comparable to ligand substitution effects in spectra.

The method effectively models spectra of polynuclear transition metal complexes.

The approach reduces computational resource needs compared to full supermolecular calculations.

Abstract

The Frenkel exciton model was adapted to describe X-ray absorption and resonant inelastic scattering spectra of polynuclear transition metal complexes by means of restricted active space self-consistent field method. The proposed approach allows to substantially decrease the requirements to computational resources if compared to a full supermolecular quantum chemical treatment. This holds true in particular in cases where the dipole approximation to the electronic transition charge density can be applied. The computational protocol was applied to the calculation of X-ray spectra of the hemin complex, which forms dimers in aqueous solution. The aggregation effects were found to be comparable to the spectral alterations due to the replacement of the axial ligand by solvent molecules.