Mean-field theory of the general-spin Ising model

Fuente: arXiv
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Main Authors: Waldorp, Lourens, Pham, Tuan, van der Maas, Han L. J.
Format: Preprint
Published: 2025
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author Waldorp, Lourens
Pham, Tuan
van der Maas, Han L. J.
author_facet Waldorp, Lourens
Pham, Tuan
van der Maas, Han L. J.
contents Motivated by modelling in physics and other disciplines, such as sociology and psychology, we derive the mean field of the general-spin Ising model from the variational principle of the Gibbs free energy. The general-spin Ising model has $2k+1$ spin values, generated by $-(k-j)/k$, with $j=0,1,2\ldots,2k$, such that for $k=1$ we obtain $-1,0,1$, for example; the Hamiltonian is identical to that of the standard Ising model. The general-spin Ising model exhibits spontaneous magnetisation, similar to the standard Ising model, but with the location translated by a factor depending on the number of categories $2k+1$. We also show how the accuracy of the mean field depends on both the number of nodes and node degree, and that the hysteresis effect decreases and saturates with the number of categories $2k+1$. Monte Carlo simulations confirm the theoretical results.
format Preprint
id arxiv_https___arxiv_org_abs_2509_21638
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Mean-field theory of the general-spin Ising model
Waldorp, Lourens
Pham, Tuan
van der Maas, Han L. J.
Statistical Mechanics
Classical Physics
Motivated by modelling in physics and other disciplines, such as sociology and psychology, we derive the mean field of the general-spin Ising model from the variational principle of the Gibbs free energy. The general-spin Ising model has $2k+1$ spin values, generated by $-(k-j)/k$, with $j=0,1,2\ldots,2k$, such that for $k=1$ we obtain $-1,0,1$, for example; the Hamiltonian is identical to that of the standard Ising model. The general-spin Ising model exhibits spontaneous magnetisation, similar to the standard Ising model, but with the location translated by a factor depending on the number of categories $2k+1$. We also show how the accuracy of the mean field depends on both the number of nodes and node degree, and that the hysteresis effect decreases and saturates with the number of categories $2k+1$. Monte Carlo simulations confirm the theoretical results.
title Mean-field theory of the general-spin Ising model
topic Statistical Mechanics
Classical Physics
url https://arxiv.org/abs/2509.21638