Excited state diabatization on the cheap using DFT: Photoinduced electron and hole transfer

TL;DR

This paper introduces a DFT-based diabatization method, { extDelta}-ALMO(MSDFT2), for accurately and efficiently modeling excited state electron and hole transfer processes in large systems, overcoming limitations of previous approaches.

Contribution

The paper presents a novel DFT-based diabatization scheme that constructs diabatic states directly from localized orbitals, enabling accurate simulation of photoinduced charge transfer.

Findings

Accurately models excited state electron and hole transfer in various systems.

Combines ALMO calculations with { extDelta}SCF and MSDFT2 for diabatic state construction.

Applicable to large, disordered condensed phase systems.

Abstract

Excited state electron and hole transfer underpin fundamental steps in processes such as exciton dissociation at photovoltaic heterojunctions, photoinduced charge transfer at electrodes, and electron transfer in photosynthetic reaction centers. Diabatic states corresponding to charge or excitation localized species, such as locally excited and charge transfer states, provide a physically intuitive framework to simulate and understand these processes. However, obtaining accurate diabatic states and their couplings from adiabatic electronic states generally leads to inaccurate results when combined with low-tier electronic structure methods, such as time dependent density functional theory (TDDFT), and exorbitant computational cost when combined with high-level wavefunction-based methods. Here we introduce a DFT-based diabatization scheme, {\Delta}-ALMO(MSDFT2), which directly constructs the diabatic states using absolutely localized molecular orbitals (ALMOs). We demonstrate that our method, which combines ALMO calculations with the {\Delta}SCF technique to construct electronically excited diabatic states and obtains their couplings with charge-transfer states using our MSDFT2 scheme, gives accurate results for excited state electron and hole transfer in both charged and uncharged systems that underlie DNA repair, charge separation in donor-acceptor dyads, chromophore-to-solvent electron transfer, and singlet fission. This framework for the accurate and efficient construction of excited state diabats and evaluation of their couplings directly from DFT thus offers a route to simulate and elucidate photoinduced electron and hole transfer in large disordered systems, such as those encountered in the condensed phase.