This work addresses the long-standing debate over fractal models of packing structure in metallic glasses (MGs). Through detailed fractal and percolation analyses of MG structures, derived from simulations spanning a range of compositions and quenching rates, we conclude that there is no fractal atomic-level structure associated with the packing of all atoms or solute-centered clusters. The results are in contradiction with conclusions derived from previous studies based on analyses of shifts in radial distribution function and structure factor peaks associated with volume changes induced by pressure and compositional variations. The interpretation of such shifts is shown to be challenged by the heterogeneous nature of MG structure and deformation at the atomic scale. Moreover, our analysis in the present work illustrates clearly the percolation theory applied to MGs, for example, the percolation threshold and characteristics of percolation clusters formed by subsets of atoms, which can have important consequences for structure-property relationships in these amorphous materials.etallic glasses (MGs) are of significant current interest because of their unique combination of mechanical properties (1-7). Although it is generally understood that these properties arise from the nature of the MG structure, the understanding of this structure, spanning atomic to medium-range scales, remains incomplete. In recent years, fractal concepts have been introduced (e.g., refs. 8-10) to describe the structure of MGs: that is, based on self-similar patterns of packing structure repeated at different length scales (11). These models have been invoked to explain (8,9,(12)(13)(14) widely observed noncubic power laws (D) correlating positions of the first sharp diffraction peak, q, or the first peak of radial distribution functions (RDFs), r, with the average atomic volume, V (or bulk atomic density, ρ = 1/V), that is:Exponents of D ≈ 2.5 or 2.3 have been measured in MGs, or the metallic melts from which they are derived based on scattering experiments and computer simulations (8,9,(12)(13)(14), in which the changes in atomic volume V have been investigated through applications of hydrostatic pressure or compositional variations. These measurements, which are in contrast to the situation for crystalline metals and alloys, where the scaling in Eq. 1 is characterized by D = 3, have led to the proposal of two distinct fractal models for the structure of MGs, associated with the packing of local clusters or atoms (see illustration of atomic configuration in Fig. 1A). In the first such model (9), it was proposed that MGs are composed of solute (minority atom)-centered clusters that are arranged on mediumrange scales in a fractal manner. This description has been the subject of debate in the literature (7,14,15), and more recently Chen et al. (8,10) proposed a description in which the individual atoms of MGs are packed according to a special class of fractal models, namely, a percolation cluster. This latter description serves to solve ...