Comment on “Collective modes and gapped momentum states in liquid Ga: Experiment, theory, and simulation”

Abstract

We show that the theoretical expressions presented in Khusnutdinoff et al. [Phys. Rev. B 101, 214312 (2020)] for the longitudinal current spectral function ${C}^{L}(k,\ensuremath{\omega})$ and the dispersion of collective excitations are not correct. Indeed, they are not compatible with the continuum limit and ${C}^{L}(k,\ensuremath{\omega}\ensuremath{\rightarrow}0)$ contradicts the continuity equation.