  In a recent article by C. Barbieri, E. Caurier, K. Langanke, and G.
Mart\'inez-Pinedo \cite{Bar.08}, low-energy dipole excitations were studied in
proton-rich $^{32,34}$Ar with random-phase approximation (RPA) and no-core
shell model (NCSM) using correlated realistic nucleon-nucleon interactions
obtained by the unitary correlation operator method (UCOM) \cite{Fel.98}. The
main objective of this Comment is to argue that the article \cite{Bar.08}
contains an inconsistency with respect to previous study of excitations in the
same UCOM-RPA framework using identical correlated Argonne V18 interaction
\cite{Paa.06}, it does not provide any evidence that the low-lying state
declared as pygmy dipole resonance in $^{32}$Ar indeed has the resonance-like
structure, and that prior to studying exotic modes of excitation away from the
valley of stability one should ensure that the model provides reliable
description of available experimental data on nuclear ground state properties
and excitations in nuclei. Although the authors aimed at testing the UCOM based
theory at the proton drip line, available experimental data that are used as
standard initial tests of theory frameworks at the proton drip line have not
been considered in the UCOM case (e.g., binding energies, one-proton separation
energies, two-proton separation energies).
