Anisotropic spatially heterogeneous dynamics on the alpha and beta relaxation time scales studied via a four-point correlation function

作者：Flenner Elijah^*; Szamel Grzegorz

来源：Physical Review E, 2009, 79(5): 051502.

DOI：10.1103/PhysRevE.79.051502

• Brownian motion
• glass transition
• liquid structure
• liquid theory
• vitrification

We examine the anisotropy of a four-point correlation function G(4)(k,r;t) and its associated structure factor S(4)(k,q;t) calculated using Brownian dynamics computer simulations of a model glass forming system. These correlation functions measure the spatial correlations of the relaxation of different particles. We examine the time and temperature dependences of the anisotropy in both functions. We find that the anisotropy is strongest at nearest-neighbor distances at time scales corresponding to the peak of the non-Gaussian parameter alpha(2)(t)=3 /[5 (2)]-1 but is still pronounced around the alpha relaxation time. We find that the structure factor S(4)(k,q;t) is anisotropic even for the lowest wave vector accessible in our simulation, suggesting that our system (and other systems commonly used in computer simulations) may be too small to extract the q -> 0 limit of the structure factor. We find that the determination of a dynamic correlation length from S(4)(k,q;t) is influenced by the anisotropy. We extract an effective anisotropic dynamic correlation length from the small q behavior of S(4)(k,q;t).

• 出版日期2009-5