Excitation spectra in fluids: How to analyze them properly

Couëdel

2020

Phys. Rev. E

In this paper we compare different theoretical approaches to describe the dispersion of collective modes in Yukawa fluids when the interparticle coupling is relatively weak, so that the kinetic and potential contributions to the dispersion relation compete with each other. A thorough comparison with the results from molecular dynamics simulation allows us to conclude that, in the investigated regime, the best description is provided by the sum of the generalized excess bulk modulus and the Bohm-Gross kinetic term.

Section: Resultsmentioning

confidence: 99%

“…To obtain the dispersion relation ω l (k), the longitudinal current fluctuation spectrum C l (k, ω) was fitted to the double-Lorentzian form [10,52]:…”

Section: Numerical Simulationsmentioning

confidence: 99%

See 1 more Smart Citation

Dispersion relations of Yukawa fluids at weak and moderate coupling

Couëdel

2020

Phys. Rev. E

“…70,71 Locating k * for various simple fluids in different parameter regimes and investigating k-gap consequences on the liquid state properties is an active area of research. [72][73][74][75][76] For our present purpose it is important that the inclination of the dispersion curve ∂ω t /∂k near the onset of the transverse mode at k > k * can be well approximated by c t . Thus, the latter is a meaningful quantity both in solid and strongly coupled fluid states.…”

Section: Sound Velocities In Different Spatial Dimensionsmentioning

confidence: 99%

Unified description of sound velocities in strongly coupled Yukawa systems of different spatial dimensionality

2019

Physics of Plasmas

Sound velocities in classical single-component fluids with Yukawa (screened Coulomb) interactions are systematically evaluated and analyzed in one-, two-, and three spatial dimensions (D = 1, 2, 3). In the strongly coupled regime the convenient sound velocity scale is given by Q 2 /∆m, where Q is the particle charge, m is the particle mass, n is the particle density, and ∆ = n −1/D is the unified interparticle distance. The sound velocity can be expressed as a product of this scaling factor and a dimension-dependent function of the screening parameter, κ = ∆/λ, where λ is the screening length. A unified approach is used to derive explicit expressions for these dimension-dependent functions in the weakly screened regime (κ 3). It is also demonstrated that for stronger screening (κ 3), the effect of spatial dimensionality virtually disappears, the longitudinal sound velocities approach a common asymptote, and a one-dimensional nearest-neighbor approximation provides a relatively good estimate for this asymptote. This result is not specific to the Yukawa potential, but equally applies to other classical systems with steep repulsive interactions. An emerging relation to a popular simple freezing indicator is briefly discussed. Overall, the results can be useful when Yukawa interactions are relevant, in particular, in the context of complex (dusty) plasmas and colloidal suspensions.

“…This phenomenon, often referred to as the k-gap in the transverse dispersion relation constitute an important fundamental research topic across disciplines. [19][20][21][22][23][24][25] The long-wavelength transverse mode dispersion relation is to a good accuracy described by 24…”

mentioning

confidence: 99%

Instantaneous shear modulus of Yukawa fluids across coupling regimes

Klumov

2020

Physics of Plasmas

The high frequency (instantaneous) shear modulus of three-dimensional Yukawa systems is evaluated in a wide parameter range, from the very weakly coupled gaseous state to the strongly coupled fluid at the crystallization point (Yukwa melt). This allows us to quantify how shear rigidity develops with increasing coupling and inter-particle correlations. The radial distribution functions (RDFs) needed to calculate the excess shear modulus have been obtained from extensive molecular dynamics (MD) simulations. MD results demonstrate that fluid RDFs appear quasi-universal on the curves parallel to the melting line of a Yukawa solid, in accordance with the isomorph theory of Roskilde-simple systems. This quasi-universality, allows to simplify considerably calculations of quantities involving integrals of the RDF (elastic moduli represent just one relevant example). The calculated reduced shear modulus grows linearly with the coupling parameter at weak coupling and approaches a quasi-constant asymptote at strong coupling. The asymptotic value at strong coupling is in reasonably good agreement with the existing theoretical approximation.