Monte Carlo study of the Pure and Dilute Baxter-Wu model

TL;DR

This study uses Wang-Landau sampling to analyze the pure and dilute Baxter-Wu models, confirming critical exponents and phase transition behaviors consistent with theoretical predictions.

Contribution

It provides the first detailed Monte Carlo analysis of the dilute Baxter-Wu model, including phase diagram and critical exponent verification.

Findings

Energy distribution shows double peaks for small samples in the pure model.

Finite size scaling confirms the specific heat exponent α=2/3.

Dilute model exhibits a crossover to a single peak and α=0.

Abstract

We studied the pure and dilute Baxter-Wu (BW) models using the Wang-Landau (WL) sampling method to calculate the Density-Of-States (DOS). We first used the exact result for the DOS of the Ising model to test our code. Then we calculated the DOS of the dilute Ising model to obtain a phase diagram, in good agreement with previous studies. We calculated the energy distribution, together with its first, second and fourth moments, to give the specific heat and the energy fourth order cumulant, better known as the Binder parameter, for the pure BW model. For small samples, the energy distribution displayed a doubly peaked shape. Finite size scaling analysis showed as expected reciprocal scaling of the positions of the peaks with L. The energy distribution yielded the expected $\alpha=2/3$ critical exponent for the specific heat. The Binder parameter minimum appeared to scale with lattice size L with an exponent $\theta_B$ equal to the specific heat exponent. Its location (temperature) showed a large correction-to-scaling term $\theta_1=0.248\pm 0.025$. For the dilute BW model we found a clear crossover to a single peak in the energy distribution even for small sizes and the expected $\alpha=0$ was recoverd.