Low-frequency dynamical heterogeneity in simulated amorphousNi0.5Zr0.5below its glass temperature: Correlations with cage volume and local order fluctuations

Abstract

From molecular dynamics simulations results are reported concerning correlations between low-frequency (lf) heterogeneous dynamics in simulated Ni0.5Zr0.5 melts at 700, 760, and 810 K, which means around the Kauzmann temperature of the model, TK approximately 750 K. A method is presented to separate lf dynamics, reflecting the slow relaxation dynamics in the vitrifying melt, and high-frequency (hf) dynamics, characteristic of the thermal fluctuations at the considered temperatures. By means of a suitable quantitative measure of the distribution of heterogeneous lf dynamics in space and time, correlation parameters are evaluated between the spatial distribution of lf dynamics and structural inhomogeneities in the thermodynamically homogeneous melt. Relevant correlations are found between lf dynamics and some involved structure quantities such as the cage volume around Ni atoms, Omega Ni, or the Theta Ni parameter which reflects the geometry of the nearest-neighbor cage around Ni atoms. Further, at 810 K there is a weak correlation between heterogeneous dynamics and fluctuations of the mean potential energy per atom and a comparable weak anticorrelation with the particle density and Ni-atom density inhomogeneities, where these three correlations decrease with decreasing temperature. The present results indicate the existence of long-living regions of enhanced Omega Ni in the structure, which may act as regions of preferential initiation of irreversible lf dynamics and slow relaxation.

Structural and dynamical heterogeneity in a glass-forming liquid

“…More recently, several studies have sought a correlation at the microscopic level, e.g. between local free volume and local mobility, with more success in some systems [10,11] than in others [12]. A notable absence of correlation between the local volume and the local Debye-Waller factor has been reported recently [13].…”

“…However, the variance around this average trend is comparable to or larger than the trend itself, making it impossible to predict what a given molecule will do based on its potential energy. Careful time averaging [10] and the use of inherent structures [16] has been shown to yield little gain in correlation. This is both perplexing and disappointing.…”

Diffusion in a Cu-Zr metallic glass studied by microsecond-scale molecular dynamics simulations

“…Therefore many studies have been carried out focusing on a long time correlation, such as the dynamical facilitation which denotes propagation of the mobile regions due to the mobility transfer of mobile particles [7]. Molecular dynamics (MD) simulations of a supercooled Ni 0.5 Zr 0.5 liquid with a time span of 1.0 µs has demonstrated marked correlations between atomic mobility and local structure parameters [8]. Regions of mobility change with time in the same system have also been revealed [9].…”

Molecular dynamics study of size effects in the compression of metallic glass nanowires

“…22 For this reason, they have been intensely investigated to shed light on both structural arrangement and dynamic behavior of atomic species. [23][24][25][26][27] This produced different reliable potentials 23,28-30 and a variety of data. The present work employs a semiempirical tightbinding ͑TB͒ potential based on the second-moment approximation to the electronic density of states.…”

“…Ni atoms behave indeed as fast diffusers in Zr. [23][24][25]47 The larger number of Ni atoms involved in bulk STZs with respect to Zr ones can be therefore regarded as the condition determining the lowest activation barrier. In other words, at any given level of local strain Ni atoms are expected to be more responsive than Zr ones.…”