Erratum: Collective modes and gapped momentum states in liquid Ga: Experiment, theory, and simulation [Phys. Rev. B 101 , 214312 (2020)]

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

“…We expected, therefore, that the correct theoretical expressions were published in the Erratum. On the contrary, in [3] the authors reported expressions identical as in an earlier paper [4] confirming in [3] that "the equations used were from our earlier theory".…”

“…One can find out in [9] how the thermo-viscoelastic model and corresponding analytical expressions can be reduced to the ones without account for energy (or heat) fluctuations. In [3] the authors claimed that their expressions for the dynamic structure factor S(k, ω) (their Eq.12) and for the dispersion of collective excitations (their Eq.15), which were identical to those reported in [4] for a single continued fraction representation ofF nn (k, z), accounted for energy fluctuations. Let us perform some simple checks.…”

“…Specifically, in their theoretical approach two types of fluctuations of conserved quantities, namely density and energy fluctuations, were missing that resulted in senseless expressions for the current spectral function and dispersion of collective excitations. In response to our criticism the authors published an Erratum [3] to their original paper explaining that "the equations referred to originally were carried over from an earlier version of the paper in error" [3]. We expected, therefore, that the correct theoretical expressions were published in the Erratum.…”

“…To emphasize the absence of energy fluctuations in the expression reported in [3] we make reference to the Generalized Collective Modes (GCM) theory for simple and manycomponent liquids, a generalised hydrodynamic approach developed by some of us [5][6][7]. The approach is based on an extented set of dynamic variables (hydrodynamic plus orthogonal to them extended ones) [8].…”

“…In (1) c T and c ∞ are the isothermal and the high-frequency speeds of acoustic modes. If one applied these asymptotes to the expression for the dispersion of correlative excitations, presented in [4] and [3], it would result in…”