Equipartition theorem and the dynamics of liquids

Levashov, V. A.; Egami, T.; Aga, Roberto S.; Morris, James R.

doi:10.1103/physrevb.78.064205

Cited by 49 publications

(78 citation statements)

References 19 publications

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“…Our results show that this increase is correlated with the increase in the value of low frequency viscosity. Thus, at T > 2T A , where T A is the potential energy landscape crossover temperature [48], stress waves of all frequencies decay on the length scales of 10 interatomic distances or less. As temperature is lowered, the increase in the ranges of propagation for the lower frequency waves is more significant than for the higher frequency waves.…”

Section: Discussionmentioning

confidence: 99%

“…The potential energy landscape crossover temperature of this system is T A ≈ 2300 (K) [48]. The mode coupling temperature is T M C ≈ 1150 (K), and the glass transition temperature is T g ≈ 950 (K).…”

Section: Details Of MD Simulations and Reduced Unitsmentioning

confidence: 99%

“…[37]). It is also useful to recall that the value of the stress auto-correlation function at zero time determines the value of the atomic level stress energy [52][53][54].…”

Section: What We See In Panelsmentioning

confidence: 99%

“…[52][53][54], as there, when the equipartition law is derived, it is assumed that different stress components on the same atom are independent. However, the derivations of the equipartition in [52][53][54] are based on the Taylor expansion and considerations of only those terms which are quadratic in atomic strain. Under this quadratic approximation, different stress components on the same atom are independent in the spherical (cubic) representation.…”

Section: What We See In Panelsmentioning

confidence: 99%

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Dependence of the atomic level Green-Kubo stress correlation function on wavevector and frequency: Molecular dynamics results from a model liquid

Levashov

2014

The Journal of Chemical Physics

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We report on a further investigation of a new method that can be used to address vibrational dynamics and propagation of stress waves in liquids. The method is based on the decomposition of the macroscopic Green-Kubo stress correlation function into the atomic level stress correlation functions. This decomposition, as was demonstrated previously for a model liquid studied in molecular dynamics simulations, reveals the presence of stress waves propagating over large distances and a structure that resembles the pair density function. In this paper, by performing the Fourier transforms of the atomic level stress correlation functions, we elucidate how the lifetimes of the stress waves and the ranges of their propagation depend on their frequency, wavevector, and temperature. These results relate frequency and wavevector dependence of the generalized viscosity to the character of propagation of the shear stress waves. In particular, the results suggest that an increase in the value of the frequency dependent viscosity at low frequencies with decrease of temperature is related to the increase in the ranges of propagation of the stress waves of the corresponding low frequencies. We found that the ranges of propagation of the shear stress waves of frequencies less than half of the Einstein frequency, extend well beyond the nearest neighbor shell even above the melting temperature. The results also show that the crossover from quasilocalized to propagating behavior occurs at frequencies usually associated with the Boson peak.

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Section: Discussionmentioning

confidence: 99%

Section: Details Of MD Simulations and Reduced Unitsmentioning

confidence: 99%

“…[37]). It is also useful to recall that the value of the stress auto-correlation function at zero time determines the value of the atomic level stress energy [52][53][54].…”

Section: What We See In Panelsmentioning

confidence: 99%

Section: What We See In Panelsmentioning

confidence: 99%

See 2 more Smart Citations

Dependence of the atomic level Green-Kubo stress correlation function on wavevector and frequency: Molecular dynamics results from a model liquid

Levashov

2014

The Journal of Chemical Physics

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“…Molecular dynamics studies were performed on a model of amorphous iron [23] with 16,584 atoms to avoid the chemical composition effects. Initially, the structure of a glass was prepared by an instant quench from a liquid at 1500 K to a glass at 700 K, followed by cooling process at 0.…”

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confidence: 99%

Universal mechanism of thermomechanical deformation in metallic glasses

et al. 2015

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Abstract:We investigated the atomistic structure of metallic glasses subjected to thermomechanical creep deformation using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in-situ, at high temperatures as a time dependent deformation in the elastic regime, and ex-situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples undergone thermo-mechanical creep can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level and the sign of the stress, demonstrating universal behavior and pointing to unique atomistic unit of anelastic deformation. The structural changes due to creep are strongly localized within the second nearest neighbors, involving only a small group of atoms. with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). Keywords 2Metallic glasses are known for their high mechanical strength and are promising as structural materials [1]. However, in spite of extensive research over many years, the atomistic mechanisms of mechanical deformation in metallic glasses remains poorly understood. A major cause of difficulty in determining the mechanism is that at room temperature deformation in metallic glasses is highly localized in narrow shear bands, and any local structural change induced by deformation is wiped out by subsequent heating [2]. On the other hand thermomechanical creep deformation, induced when metallic glass is subjected to stress at elevated temperatures approaching the glass transition, is spatially homogeneous and thus easier to study [e.g. 3]. It is known that creep deformation leaves the sample in a structurally anisotropic state because of anelastic deformation resulting in bond-orientational anisotropy [4,5]. In this work we focus on the structural aspects of the thermo-mechanical creep deformation by using high energy x-ray diffraction and we show that when appropriately scaled, the structural anisotropy induced by creep deformation is independent of time and stress, implying that a universal mechanism of creep deformation exists.In crystalline materials anelastic and plastic deformation is caused by the movement of lattice defects. In glasses, on the other hand, defects cannot be easily and uniquely identified.Phenomenologically the creep is explained in terms of formation and interaction of the shear transformation zones (STZs) [6,7]. STZ is an important concept used in explaining mechanical deformation and flow of metallic glasses [8,9,10,11]. Howev...

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Ubiquitiform Hotspot Ignition Model of PBX for Shock Initiation

Chun

Duan

et al. 2021

Propellants Explo Pyrotec

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In this study, a ubiquitiform hotspot ignition model with cross‐scale characteristics is proposed to describe the ignition stage of PBX, which can account for heterogeneous effects. Firstly, a ubiquitiform model of hotspot intensity is obtained. The model can describe the hotspot information after PBX is impacted. In which, a hotspot distribution model based on the nested ubiquitiform model of explosives is used to characterize geometric properties of hotspot, including the size and location of hotspot; and the Weibull statistical distribution function is used to describe the distribution of hotspot intensity. Then, combining the ubiquitiform model of hotspot intensity with Arrhenius model, the ubiquitiform hotspot ignition model is developed to characterize the ignition stage of PBX. Finally, it is found that the equivalent reaction rate constants calculated by our ignition model are in good agreement with the previous experimental data.

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Equipartition theorem and the dynamics of liquids

Cited by 49 publications

References 19 publications

Dependence of the atomic level Green-Kubo stress correlation function on wavevector and frequency: Molecular dynamics results from a model liquid

Dependence of the atomic level Green-Kubo stress correlation function on wavevector and frequency: Molecular dynamics results from a model liquid

Universal mechanism of thermomechanical deformation in metallic glasses

Ubiquitiform Hotspot Ignition Model of PBX for Shock Initiation

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