  Quantum embedding methods have recently developed significantly to model
large molecular structures. This work proposes a novel wave function theory in
density functional theory (WTF-in-DFT) embedding scheme based on pair-coupled
cluster doubles (pCCD)-type methods. While pCCD can reliably describe
strongly-correlated systems with mean-field-like computational cost, the large
extent of dynamic correlation can be accounted for by (linearized)
coupled-cluster corrections on top of the pCCD wave function. Here we focus on
the linearized coupled-cluster singles and doubles (LCCSD) ansatz for
electronic ground states and its extension to excited states within the
equation of motion (EOM) formalism. We test our EOM-pCCD-LCCSD-in-DFT approach
for the vertical excitation energies of the hydrogen-bonded water--ammonia
complex and uranyl tetrahalides (UO$_2$X$_4^{2-}$, X=F, Cl, Br). Furthermore,
we assess the quality of the embedding potential using an orbital entanglement
and correlation analysis. The approximate models successfully capture changes
in the excitation energies going from bare fragments to supramolecular
structures and represent a promising computation model for excited states in
large molecular systems.
