Three-Dimensional Random Voronoi Tessellations: From Cubic Crystal Lattices to Poisson Point Processes


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Abstract

We perturb the simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) structures with a spatial Gaussian noise whose adimensional strength is controlled by the parameter α and analyze the statistical properties of the cells of the resulting Voronoi tessellations using an ensemble approach. We concentrate on topological properties of the cells, such as the number of faces, and on metric properties of the cells, such as the area, volume and the isoperimetric quotient. The topological properties of the Voronoi tessellations of the SC and FCC crystals are unstable with respect to the introduction of noise, because the corresponding polyhedra are geometrically degenerate, whereas the tessellation of the BCC crystal is topologically stable even against noise of small but finite intensity. Whereas the average volume of the cells is the intensity parameter of the system and does not depend on the noise, the average area of the cells has a rather interesting behavior with respect to noise intensity. For weak noise, the mean area of the Voronoi tessellations corresponding to perturbed BCC and FCC perturbed increases quadratically with the noise intensity. In the case of perturbed SCC crystals, there is an optimal amount of noise that minimizes the mean area of the cells. Already for a moderate amount of noise (α>0.5), the statistical properties of the three perturbed tessellations are indistinguishable, and for intense noise (α>2), results converge to those of the Poisson-Voronoi tessellation. Notably, 2-parameter gamma distributions constitute an excellent model for the empirical pdf of all considered topological and metric properties. By analyzing jointly the statistical properties of the area and of the volume of the cells, we discover that also the cells shape, measured by the isoperimetric quotient, fluctuates. The Voronoi tessellations of the BCC and of the FCC structures result to be local maxima for the isoperimetric quotient among space-filling tessellations, which suggests a weaker form of the recently disproved Kelvin conjecture. Moreover, whereas the size of the isoperimetric quotient fluctuations go to zero linearly with noise in the SC and BCC case, the decrease is quadratic in the FCC case. Correspondingly, anomalous scaling relations with exponents larger than 3/2 are observed between the area and the volumes of the cells for all cases considered, and, except for the FCC structure, also for infinitesimal noise. In the Poisson-Voronoi limit, the exponent is ∼1.67. The anomaly in the scaling indicates that large cells preferentially feature large isoperimetric quotients. The FCC structure, in spite of being topologically unstable, results to be the most stable against noise when the shape—as measured by the isoperimetric quotient—of the cells is considered. These scaling relations apply only for a finite range and should be taken as descriptive of the bulk statistical properties of the cells. As the number of faces is strongly correlated with the sphericity (cells with more faces are bulkier), the anomalous scaling is heavily reduced when we perform power law fits separately on cells with a specific number of faces.

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