Computation of Microcanonical Entropy at Fixed Magnetization Without Direct Counting

We discuss a method to compute the microcanonical entropy at fixed magnetization without direct counting. Our approach is based on the evaluation of a saddle-point leading to an optimization problem. The method is applied to a benchmark Ising model with simultaneous presence of mean-field and neares...

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Bibliographic Details
Published in:Journal of statistical physics 2021-08, Vol.184 (2), Article 21
Main Authors: Campa, Alessandro, Gori, Giacomo, Hovhannisyan, Vahan, Ruffo, Stefano, Trombettoni, Andrea
Format: Article
Language:English
Subjects:
Analysis
Couplings
Entropy
Ising model
Magnetization
Mathematical and Computational Physics
Optimization
Physical Chemistry
Physics
Physics and Astronomy
Quantum Physics
Saddle points
Statistical Physics and Dynamical Systems
Theoretical
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Summary:We discuss a method to compute the microcanonical entropy at fixed magnetization without direct counting. Our approach is based on the evaluation of a saddle-point leading to an optimization problem. The method is applied to a benchmark Ising model with simultaneous presence of mean-field and nearest-neighbour interactions for which direct counting is indeed possible, thus allowing a comparison. Moreover, we apply the method to an Ising model with mean-field, nearest-neighbour and next-nearest-neighbour interactions, for which direct counting is not straightforward. For this model, we compare the solution obtained by our method with the one obtained from the formula for the entropy in terms of all correlation functions. This example shows that for general couplings our method is much more convenient than direct counting methods to compute the microcanonical entropy at fixed magnetization.
ISSN:0022-4715
1572-9613
DOI:10.1007/s10955-021-02809-y