An Efficient Monte-Carlo Method for Calculating Free-Energy in Long-Range Interacting Systems

TL;DR

This paper introduces a novel Monte-Carlo approach combining Wang-Landau and stochastic cutoff methods to efficiently compute free energy in large, long-range interacting systems without approximations.

Contribution

The paper presents a new Monte-Carlo method that efficiently calculates free energy in long-range systems, applicable to large system sizes, with a detailed comparison to existing methods.

Findings

Successfully applied to a 16^3 spin magnetic dipolar system.

Achieves reasonable computational time without approximations.

Provides insights into the advantages and disadvantages compared to traditional Wang-Landau methods.

Abstract

We present an efficient Monte-Carlo method for long-range interacting systems to calculate free energy as a function of an order parameter. In this method, a variant of the Wang-Landau method regarding the order parameter is combined with the stochastic cutoff method, which has recently been developed for long-range interacting systems. This method enables us to calculate free energy in long-range interacting systems with reasonable computational time despite the fact that no approximation is involved. This method is applied to a three-dimensional magnetic dipolar system to measure free energy as a function of magnetization. By using the present method, we can calculate free energy for a large system size of $16^3$ spins despite the presence of long-range magnetic dipolar interactions. We also discuss the merits and demerits of the present method in comparison with the conventional Wang-Landau method in which free energy is calculated from the joint density of states of energy and order parameter.