  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.

Chemical Physics