Focusing on C 3 , the phonons have a negative frequency (*) along i.e., along the vertical direction of the BZ indicating instability towards a transient state, i.e., the structure could be unstable, and a possible phase transition could occur. However, we note that in the "qtz" C 3 paper the authors claimed all positive phonons without showing corresponding band structures. While we do not question their results, we point out that in the same calculation protocols for all four carbon forms, the other carbon stoichiometries show no negative phonons and they are considered to be dynamically stable. We propose that the extension of the carbon stoichiometry in the presently studied series is a stabilizing factor of the carbon structure.