Finite-size scaling behavior of the magnetization distribution for 5d Ising model

Ziya Merdan, Nida Aras, Cihan Kürkçü

K. K. Mon

We address the long-standing disagreement between renormalization group (RG) and Monte Carlo (MC) study of finite-size scaling for the order parameter distribution function of the 5D Ising model. MC study finds disagreement between the RG and MC on the fourth-order Binder cumulant. Two new results are presented here. First, we compare the RG predictions for the first and third absolute moment to MC data. Good agreement and finite-size corrections which are much smaller than for the cumulant are found. Second, we observe that the size dependence of the corrections is consistent with the RG square-root law, which is slow. This, together with a large correction amplitude for the cumulant, provide a possible explanation for prior disagreement.

Yusuke Tomita, Yutaka Okabe, Chin‐Kun Hu

Based on the connection between the Ising model and a correlated percolation model, we calculate the distribution function for the fraction (c) of lattice sites in percolating clusters in subgraphs with n percolating clusters, f(n)(c), and the distribution function for magnetization (m) in subgraphs with n percolating clusters, p(n)(m). We find that f(n)(c) and p(n)(m) have very good finite-size scaling behavior and that they have universal finite-size scaling functions for the model on square, plane triangular, and honeycomb lattices when aspect ratios of these lattices have the proportions 1:square root[3]/2:square root[3]. The complex structure of the magnetization distribution function p(m) for the system with large aspect ratio could be understood from the independent orientations of two or more percolation clusters in such a system.

Kazuyuki Matsumoto, Yasuhiro Akutsu

Nevzat AKTEKİN

Louis Colonna-Romano, Harvey Gould, W. Klein

Although the fully connected Ising model does not have a length scale, we show that the critical exponents for thermodynamic quantities such as the mean magnetization and the susceptibility can be obtained using finite size scaling with the scaling variable equal to N, the number of spins. Surprisingly, the mean value and the most probable value of the magnetization are found to scale differently with N at the critical temperature of the infinite system, and the magnetization probability distribution is not a Gaussian, even for large N. Similar results inconsistent with the usual understanding of mean-field theory are found at the spinodal. We relate these results to the breakdown of hyperscaling and show that hyperscaling can be restored by increasing N while holding the Ginzburg parameter rather than the temperature fixed, or by doing finite size scaling at the pseudocritical temperature where the susceptibility is a maximum for a given value of N. We conclude that finite size scaling for the fully connected Ising model yields different results depending on how the mean-field limit is approached.