  When a vacancy is created in an inner-valence orbital of a dimer of atoms or
molecules, the resulting species can undergo interatomic/intermolecular
Coulombic decay (ICD): the hole is filled through a relaxation process that
leads to a doubly ionized cluster with two positively charged atoms or
molecules. Since they are subject to electronic decay, inner-valence ionized
states are not bound states but electronic resonances whose transient nature
can only be described with special quantum-chemical methods. In this work, we
explore the capacity of equation-of-motion coupled-cluster theory combined with
two techniques from non-Hermitian quantum mechanics, complex basis functions
and Feshbach-Fano projection, to describe ICD. To this end, we compute decay
rates of several dimers: Ne_2, NeAr, NeMg, and (HF)_2, among which the energy
of the outgoing electron varies between 0.3 eV and 16 eV. We observe that both
methods deliver better results when the outgoing electron is fast, but the
characteristic R^{-6} distance dependence of the ICD width is captured much
better with complex basis functions.
