  Localized molecular orbitals are often used for the analysis of chemical
bonds, but they can also serve to efficiently and comprehensibly compute linear
response properties. While conventional canonical molecular orbitals provide an
adequate basis for the treatment of excited states, a chemically meaningful
identification of the different excited-state processes is difficult within
such a delocalized orbital basis. In this work, starting from an initial set of
supermolecular canonical molecular orbitals, we provide a simple one-step
top-down embedding procedure for generating a set of orbitals which are
localized in terms of the supermolecule, but delocalized over each subsystem
composing the supermolecule. Using an orbital partitioning scheme based on such
sets of localized orbitals, we further present a procedure for the construction
of local excitations and charge-transfer states within the linear response
framework of time-dependent density functional theory (TDDFT). This procedure
provides direct access to approximate diabatic excitation energies and, under
the Tamm--Dancoff approximation, also their corresponding electronic couplings
-- quantities that are of primary importance in modelling energy transfer
processes in complex biological systems. Our approach is compared with a
recently developed diabatization procedure based on subsystem TDDFT using
projection operators, which leads to a similar set of working equations.
Although both of these methods differ in the general localization strategies
adopted and the type of basis functions (Slaters vs. Gaussians) employed, an
overall decent agreement is obtained.
