The occurrence of a propagation gap in the acoustic excitations of a liquid is excluded by Wax and Bryk (2013 J. Phys.: Condens. Matter 25 325104). The requirement of a finite second frequency moment for the dynamic structure factor is used to come to this conclusion. We show here that this requirement does not conflict with the existence of overdamped, nonpropagating modes which give rise to spectra that do not contain inelastic components. Such a behaviour has indeed been detected in the analysis of the collective dynamics of several liquids, carried out by using well-established sum-rule-compliant S(q, ω) models.
Comment on ‘An effective fitting scheme for the dynamic structure of pure liquids’ / U. Bafile; E. Guarini; F. Barocchi. - In: JOURNAL OF PHYSICS. CONDENSED MATTER. - ISSN 0953-8984. - STAMPA. - 26:(2014), pp. 168001-168002. [10.1088/0953-8984/26/16/168001]
Comment on ‘An effective fitting scheme for the dynamic structure of pure liquids’
GUARINI GRISALDI TAJA O DEL TAJA, ELEONORA;BAROCCHI, FABRIZIO
2014
Abstract
The occurrence of a propagation gap in the acoustic excitations of a liquid is excluded by Wax and Bryk (2013 J. Phys.: Condens. Matter 25 325104). The requirement of a finite second frequency moment for the dynamic structure factor is used to come to this conclusion. We show here that this requirement does not conflict with the existence of overdamped, nonpropagating modes which give rise to spectra that do not contain inelastic components. Such a behaviour has indeed been detected in the analysis of the collective dynamics of several liquids, carried out by using well-established sum-rule-compliant S(q, ω) models.
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