The probability distribution of the largest cluster size is studied within a three-dimensional bond percolation model on small lattices. Cumulants of the distribution exhibit distinct features near the percolation transition (pseudocritical point), providing a method for its identification. The location of the critical point in the continuous limit can be estimated without variation of the system size. This method is remarkably insensitive to finite-size effects and may be applied even for a very small system. The possibility of using various measurable quantities for sorting events makes the procedure useful in studying clusterization phenomena, in particular nuclear multifragmentation. Finite-size scaling and \ensuremath{\Delta}-scaling relations are examined. The role of surface effects is evaluated by a comparison of results for free and periodic boundary conditions.
The probability distribution of the largest cluster size is studied within a three-dimensional bond percolation model on small lattices. Cumulants of the distribution exhibit distinct features near the percolation transition (pseudocritical point), providing a method for its identification. The location of the critical point in the continuous limit can be estimated without variation of the system size. This method is remarkably insensitive to finite-size effects and may be applied even for a very small system. The possibility of using various measurable quantities for sorting events makes the procedure useful in studying clusterization phenomena, in particular nuclear multifragmentation. Finite-size scaling and \ensuremath{\Delta}-scaling relations are examined. The role of surface effects is evaluated by a comparison of results for free and periodic boundary conditions.
Order parameter fluctuations (the largest cluster size distribution) are studied within a three-dimensional bond percolation model on small lattices. Cumulant ratios measuring the fluctuations exhibit distinct features near the percolation transition (pseudocritical point), providing a method for its identification. The location of the critical point in the continuous limit can be estimated without variation of the system size. This method is remarkably insensitive to finite-size effects and may be applied even for a very small system. The possibility of using various measurable quantities for sorting events makes the procedure useful in studying clusterization phenomena, in particular nuclear multifragmentation. Finite-size scaling and delta-scaling relations are examined. The model shows inconsistency with some of the delta-scaling expectations. The role of surface effects is evaluated by comparing results for free and periodic boundary conditions.
We examine the average cluster distribution as a function of lattice probability for a very small (L=6) lattice and determine the scaling function of three-dimensional percolation. The behavior of the second moment, calculated from the average cluster distribution of L=6 and L=63 lattices, is compared to power-law behavior predicted by the scaling function. We also examine the finite-size scaling of the critical point and the size of the largest cluster at the critical point. This analysis leads to estimates of the critical exponent $\ensuremath{\nu}$ and the ratio of critical exponents $\ensuremath{\beta}/\ensuremath{\nu}$.
Abstract Universality, encompassing critical exponents, scaling functions, and dimensionless quantities, is fundamental to phase transition theory. In finite systems, universal behaviors are also expected to emerge at the pseudocritical point. Focusing on two-dimensional percolation, we show that the size distribution of the largest cluster asymptotically approaches to a Gumbel form in the subcritical phase, a Gaussian form in the supercritical phase, and transitions within the critical finite-size scaling window. Numerical results indicate that, at consistently defined pseudocritical points, this distribution exhibits a universal form across various lattices and percolation models (bond or site), within error bars, yet differs from the distribution at the critical point. The critical polynomial, universally zero for two-dimensional percolation at the critical point, becomes nonzero at pseudocritical points. Nevertheless, numerical evidence suggests that the critical polynomial, along with other dimensionless quantities such as wrapping probabilities and Binder cumulants, assumes fixed values at the pseudocritical point that are independent of the percolation type (bond or site) but vary with lattice structures. These findings imply that while strict universality breaks down at the pseudocritical point, certain extreme-value statistics and dimensionless quantities exhibit quasi-universality, revealing a subtle connection between scaling behaviors at critical and pseudocritical points.
Using Monte Carlo methods and finite-size scaling, we investigate surface critical phenomena in the bond-percolation model on the simple-cubic lattice with two open surfaces in one direction. We decompose the whole lattice into percolation clusters and sample the surface and bulk dimensionless ratios Q1 and Qb, defined on the basis of the moments of the cluster-size distribution. These ratios are used to determine critical points. At the bulk percolation threshold pbc, we determine the surface bond-occupation probability at the special transition as p(s)1c = 0.418 17(2), and further obtain the corresponding surface thermal and magnetic exponents as y(s)t1 = 0.5387(2) and y(s)h1 = 1.8014(6), respectively. Next, from the pair correlation function on the surfaces, we determine y(o)h1 = 1.0246(4) and y(e)h1 = 1.25(6) for the ordinary and the extraordinary transition, respectively, of which the former is consistent with the existing result y(o)h1 = 1.024(4). We also numerically derive the line of surface phase transitions occurring at pb < pbc, and determine the pertinent asymptotic values of the universal ratios Q1 and Qb.
We study the ratio of the number of sites in the largest and second largest clusters in random percolation. Using the scaling hypothesis that the ratio <M1>/<M2> of the mean cluster sizes M1 and M2 scales as f ((p - pc) L1/ν), we employ finite-size scaling analysis to find that <M1>/<M2> is nonuniversal with respect to the boundary conditions imposed. The mean <M1/M2> of the ratios behaves similarly although with a distinct critical value reflecting the relevance of mass fluctuations at the percolation threshold. These zero exponent ratios also allow for reliable estimates of the critical parameters at percolation from relatively small lattices.
Abstract We present a unifying, consistent, finite-size-scaling picture for percolation theory bringing it into the framework of a general, renormalization-group-based, scaling scheme for systems above their upper critical dimensions d c . Behaviour at the critical point is non-universal in d > d c = 6 dimensions. Proliferation of the largest clusters, with fractal dimension 4, is associated with the breakdown of hyperscaling there when free boundary conditions are used. But when the boundary conditions are periodic, the maximal clusters have dimension D = 2 d /3, and obey random-graph asymptotics. Universality is instead manifested at the pseudocritical point, where the failure of hyperscaling in its traditional form is universally associated with random-graph-type asymptotics for critical cluster sizes, independent of boundary conditions.