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Density of states and dynamical crossover in a dense fluid revealed by exponential mode analysis of the velocity autocorrelation function

Autor(en)
S. Bellissima, M. Neumann, E. Guarini, U. Bafile, F. Barocchi
Abstrakt

Extending a preceding study of the velocity autocorrelation function (VAF) in a simulated Lennard-Jones fluid [Phys. Rev. E 92, 042166 (2015)] to cover higher-density and lower-temperature states, we show that the recently demonstrated multiexponential expansion method allows for a full account and understanding of the basic dynamical processes encompassed by a fundamental quantity as the VAF. In particular, besides obtaining evidence of a persisting long-time tail, we assign specific and unambiguous physical meanings to groups of exponential modes related to the longitudinal and transverse collective dynamics, respectively. We have made this possible by consistently introducing the interpretation of the VAF frequency spectrum as a global density of states in fluids, generalizing a solid-state concept, and by giving to specific spectral components, obtained through the VAF exponential expansion, the corresponding meaning of partial densities of states relative to specific dynamical processes. The clear identification of a high-frequency oscillation of the VAF with the near-top excitation frequency in the dispersion curve of acoustic waves is a neat example of the power of the method. As for the transverse mode contribution, its analysis turns out to be particularly important, because the multiexponential expansion reveals a transition marking the onset of propagating excitations when the density is increased beyond a threshold value. While this finding agrees with the recent literature debating the issue of dynamical crossover boundaries, such as the one identified with the Frenkel line, we can add detailed information on the modes involved in this specific process in the domains of both time and frequency. This will help obtain a still missing full account of transverse dynamics, in both its nonpropagating and propagating aspects which are linked through dynamical transitions depending on both the thermodynamic states and the excitation wave vectors.

Organisation(en)
Computergestützte Physik und Physik der Weichen Materie
Externe Organisation(en)
Università degli Studi di Firenze, Consiglio Nazionale delle Ricerche
Journal
Physical Review E
Band
95
Anzahl der Seiten
14
ISSN
1539-3755
DOI
https://doi.org/10.1103/PhysRevE.95.012108
Publikationsdatum
01-2017
Peer-reviewed
Ja
ÖFOS 2012
103015 Kondensierte Materie, 103029 Statistische Physik
Schlagwörter
ASJC Scopus Sachgebiete
Condensed Matter Physics, Statistical and Nonlinear Physics, Statistics and Probability
Link zum Portal
https://ucrisportal.univie.ac.at/de/publications/547b5178-afff-4753-8a71-c420e5f65553