Short to long-range charge-transfer excitations in the zincbacteriochlorin-bacteriochlorin complex: a Bethe-Salpeter study

TL;DR

This study employs the Bethe-Salpeter formalism to accurately compute charge transfer excitation energies in a photosynthetic complex, outperforming standard methods and correctly modeling long-range Coulomb interactions without adjustable parameters.

Contribution

The paper demonstrates that the Bethe-Salpeter approach accurately predicts charge transfer excitations and their asymptotic behavior, surpassing traditional TDDFT calculations in a complex biological system.

Findings

Charge transfer excitations are correctly positioned above intramolecular transitions.

The method reproduces the Coulomb behavior at long distances.

The approach works without adjustable parameters across different environments.

Abstract

We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbacteriochlorin dyad, a paradigmatic photosynthetic complex. In great contrast with standard timedependent density functional theory calculations with (semi)local kernels, charge transfer excitations are correctly located above the intramolecular Q-bands transitions found to be in excellent agreement with experiment. Further, the asymptotic Coulomb behavior towards the true quasiparticle gap for charge transfer excitations at long distance is correctly reproduced, showing that the present scheme allows to study with the same accuracy intramolecular and charge transfer excitations at various spatial range and screening environment without any adjustable parameter.