Collective acoustic modes as renormalized damped oscillators: Unified description of neutron and x-ray scattering data from classical fluids

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Ubaldo Bafile,¹ Eleonora Guarini,² and Fabrizio Barocchi^2,3
¹Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano, I-50019 Sesto Fiorentino, Italy
²CNR-INFM and CRS-Soft, c/o Dipartimento di Fisica, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy
³Dipartimento di Fisica, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Italy

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Received 23 January 2006; published 26 June 2006

Inthe Q range where inelastic x-ray and neutron scattering areapplied to the study of acoustic collective excitations in fluids,various models of the dynamic structure factor S(Q, omega ) generalize indifferent ways the results obtained from linearized-hydrodynamics theory in theQ --> 0 limit. Here we show that the models most commonlyfitted to experimental S(Q, omega ) spectra can be given a unifiedformulation. In this way, direct comparisons among the results obtainedby fitting different models become now possible to a muchlarger extent than ever. We also show that a consistentdetermination of the dispersion curve and of the propagation Qrange of the excitations is possible, whichever model is used.We derive an exact formula which describes in all casesthe dispersion curve and allows for the first quantitative understandingof its shape, by assigning specific and distinct roles tothe various structural, thermal, and damping effects that determine theQ dependence of the mode frequencies. The emerging picture describesthe acoustic modes as Q-dependent harmonic oscillators whose characteristic frequencyis explicitly renormalized in an exact way by the relaxationprocesses, which also determine, through the widths of both theinelastic and the elastic lines, the whole shape of collective-excitationspectra.

URL:	http://link.aps.org/doi/10.1103/PhysRevE.73.061203
DOI:	10.1103/PhysRevE.73.061203
PACS:	61.20.Lc; 61.20.Gy; 61.12.Ex; 61.10.Eq 61.20.Lc Time-dependent properties of liquid structure; relaxation 61.20.Gy Theory and models of liquid structure 61.12.Ex Neutron scattering (including small-angle scattering) 61.10.Eq X-ray scattering including small-angle scattering YEAR: 2006
KEYWORDS:	liquid structure, liquid theory, X-ray scattering, neutron diffraction, damping

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Erratum

Erratum: Collective acoustic modes as renormalized damped oscillators: Unified description of neutron and x-ray scattering data from classical fluids [Phys. Rev. E 73, 061203 (2006)]
Ubaldo Bafile, Eleonora Guarini, and Fabrizio Barocchi
Phys. Rev. E 74, 059902 (E) (2006)